£NITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 597 

Contribation from the Bureau of Entomology 
L. O. HOWARD, Chief 




Washington, D. C. 



PROFESSIONAL PAPER 



April 9, 1918 



SOME BIOLOGICAL AND CONTROL STUDIES 

OF GASTROPHILUS HAEMORRHOIDALIS AND 

OTHER BOTS OF HORSES 

By 

W. E. DOVE, Scientific Assistant 
Insects Affecting Domestic Animals 



CONTENTS 



Page 
1 
2 
2 
3 



Introduction 

Brief Life History of Gastrophilus 

Histoiicai 

Species Differentiation 

Distribution in the United States and 
Probable Dispersion 5 

Larval Collecticns and Rearing Tech- 
nique 6 

Larval Infestation and Injuries .... 6 

Bot-fly Annoyance 13 



Page 

Natural Protection of Horses .... 14 

Seasonal History of Gastrophilus ... 15 

Gcstrophilus haemorrhoidalis Linn . 16 

Gaatrophilua nasalis Linn 30 

Gastrophilus intestinalia DeGeer . . 32 
Effect of Death of Host upon Gltstro- 

philus Larvte 34 

Control Studies 35 

Summary 48 

Bibliography 60 




WASHINGTON 

GOVERNMENT PRINTING OFFICK 

1918 



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UNITED STATES DEPARTMENT OF AGRICULTURE 




s^Js-'^j^u 



BULLETIN No. 597 



Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 




j^^/s-'^Zru 



Washington, D. C. 



PROFESSIONAL PAPER. 



April 9, 1918 



SOME BIOLOGICAL AND CONTROL STUDIES OF 
GASTROPHILUS HAEMORRHOIDALIS AND 
OTHER BOTS OF HORSES/ 

By W. E. Dove, Scientific Assistant, Insects Affecting Domestic Animals. 



CONTENTS. 



Introduction 1 

Brict life history of Gastrophilus 2 

Historical 2 

Species differentiation 3 

Distribution in the United States and prob- 
able dispersion 5 

Larval collections and rearing technique ... 5 

Larval infestation and injuries 6 

Bot-fly annoyance 13 

Natural protection of horses ^- 14 



Page. 

Seasonal history of G astrophilus 15 

Gastrophilus hacmorrhoidalis (Linnaeus) 16 

Gastrophilus nasalis (Linnaeus) 30 

Gastrophilus intestinalis (De Geer) 32 

Effect of death of host upon Gastrophilus 

larvffi 34 

Control studies 35 

Summary 48 

Bibliography 50 



INTRODUCTION. 

In compliance with requests from farmers and horse breeders of 
the Dakotas and Montana regarding " fly annoyance "" to horses, a 
survey of conditions was made in the autumn of 1914 by Mr. F. C. 
Bishopp. Under the direction of Dr. W. D. Hunter and the super- 
vision of Mr. Bishopp, investigations were undertaken in the follow- 
ing summer upon the European Gastrophilus haemorrhoidalis, com- 
monly known in that section as the " nose-fly." 

The preliminary investigations in the summer of 1915 revealed 
the fact that the concentration of horses in pastures had rendered 
breeding conditions practically ideal for bot-flies, and that a most 
serious Hy nuisance had developed which implicated three species of 
Gastrophilus. This concentration of horses in pastures may be 
attributed in part to the advent of gas engines, automobiles, and 
tractors, and to maximum prices, which has encouraged the breeder 

»Mr. H. B. Bradford made the drawing illustrating the eggs of Gastrophilus, and 
Mr. W. N. Dovener made those illustrating the larvse and dorsal aspects of the adults. 
Many of the photographs were made by Mr. A. K. Pettit. 

11216°— 18— Bull. 597 1 1 



2 BULLETIN 597, U. S. DEPAETMEISTT OF AGEICULTURE. 

to meet the great demand for arm_y horses. Within the nose-fly dis- 
trict is to be found one of the hirgest horse-sale points in the world. 

BRIEF LIFE HISTORY OF GASTROPHILUS. 

Our knoAYledge of the life histories and habits of these insect 
pests, which is always essential to successful control, is confined for 
the most part to the classical accounts of Bracy Clark in 1797 and 
subsequently, although later writers have added important details. 

l^Tien the female of G astro 'pJiilus intestinalis (G. equi) becomes 
sexually mature it is most often observed hovering near the inside 
of the knee of a horse, where by preference the eggs are deposited. 
After a few days, when the larvae develop within the eggs, the horse 
by scratching the forelegs with the teeth provides sujfiicient moisture 
and friction to remove the operculum or small cap of the eggs and 
inadvertently the larvae are taken within the mouth. The empty 
eggshells remain attached to the hairs of the legs, whereas the 
larvae are carried with the food or water to the stomach, where 
attachment to the stomach walls takes place. Here they undergo 
development during the autumn, winter, and spring months, and 
later are passed from the horse with the manure. At this stage pupa- 
tion ensues and adult flies are produced. 

The other species of bots also spend similar larval periods in the 
animal, but have habits peculiar to the particular species. 

HISTORICAL. 

The literature containing historical references to the Oestridae 
carries one to a most remote time. The ancient Greeks and the 
Latins refer to " an unspeakable fright of cattle," though later 
writers are not agreed as to whether it was produced by an oestrid 
or a tabanid. It is certain, however, that Aristotle knew the forms 
found in the throats of deer. 

The Greek veterinarians Theomnestus and Absyrtus give us the 
earliest record which could be referred to Gastrophilus when they 
write of the "biting worms which fix themselves to the anus of the 
horse." In order to destroy them it was recommended that they 
be torn from the anus with the fingers and covered with hot ashes 
and puh'erized salt. 

Malpighi in 1697 gave the first description of a gastrophilid larva 
taken from the stomach of an ass. According to Jol}', it belonged to 
the species G. intestinalis De Geer, while to Brauer it was G. flavipes 
Olivier. Gaspari published an erroneous opinion that G. haemorrho- 
idah's deposited its eggs in the rectum of the horse during def- 
ecation, and that the larvae migrated to the stomach until about 
fully developed. Vallisnieri and Reaumur made the same erroneous 
diagnosis. 



GASTROPHILUS HAEMOEEHOIDALIS AND OTHEE BOTS. 



Linnaeus, Fabricius, and De Geer occupied themselves with the 
early classification, and not until 1797, with Bracy Clark, does the 
natural history of the Oestridse truly commence. To this historical 
work of Bracy Clark a few additions, many of which are cited in the 
bibliography, have been made by subsequent writers. 

In conformity with the rules of nomenclature and following the 
reestablishment of the Linnaean designation " intestinalis " by Guyot, 
" Gastrophilus intestinalis " is given preference rather than " Gastro- 
philus ec[idP 

Aside from priority, the specific name " eqid " is not reliable, since 
there are several spe- 
cies of Gastrophilus 
which infest the 
horse; moreover "m- 
testinul'is " has been 
adopted by a number 
of dependable au- 
thorities. 

SPECIES DIFFEREN- 
TIATION. 



The 



ejiss. 



larvae, 
are so 




anCl aQUltS uic su Vig. l. — GastropUUus nasalis: Female. Oviposits com- 
easily distino"uishable monly under the jaws of horses. Greatly enlarged. 
, . ^ 4.1 . -J. (Original.) 

in this genus that it 

does not require a study of detailed descriptions to enable a student 
to determine the species. (Figs. 1, 2, 3.) Prof. Carman's key to the 
wing venation, a reliable index to the species, is here quoted. 

Key to Wing Venation of Gastrophilus Spp. 

1. Discoidal cell not closed by a cross vein G. pecorum. 

Discoidal cell closed by a cross vein 2 

2. Wings marked with brown G. intestinalis. 

Wings not marked witli brown 3 

3. Anterior basal cell nearly or quite equal to the discoidal cell in 

length G. nasalis. 

Anterior basal cell markedly shorter than the discoidal 

cell G. haemorrhoidalis. 

The cloudy wings of G. intestinalis and its habit of depositing 
upon any convenient portion of the horse where it is not disturbed, 
but most commonly on the forelegs, will enable one to distinguish 
it most readily. 

G. nasalis is smaller than G. intestinalis, densely hair}", with the 
thorax yellowish red or rust colored. Its most common place of 
oviposition is under the jaws, but it is sometimes observed to oviposit 



BULLETIN 597^ U. S. DEPARTMENT OF AGEICULTUEE. 



upon the flanks or forelegs of the animal. Unlike G. intestinalis, 
it does not remain near the animal prior to the deposition of a 
second egg. 

G. haemorrhoidalis is easily distinguished by the bright orange 
red on the tip of the abdomen. The thorax above is olive gray and 
hairy, with a black band behind the suture. The base of the abdo- 
men is whitish and the mid- 
dle blackish, which is in 
strange contrast with the 
orange red of the end. It 
deposits only upon the small 
hairs on the lips of horses 
and mules. 

The males of G. intesti- 
nalis and G. haemorrhoi- 
dalis are often found await- 
ing the approach of females 
to the horses, and when they 
arrive the flies copulate. 

The species characteristics 
of the eggs of the three 
species occurring in the 




Fig. 2. — GastropMlus haemorrhoidalis: Female. 
Oviposits only upon the small hair on the lips 
of horses, preferably the portions moistened by 
saliva. Greatly enlarged. (Original.) 



United States can best be observed by referring to the illustration 
(fig. 3). While G. intestinaUs is usually attached about one-half its 
length to the hair, G. nasalis is attached almost its entire length. 
G. haemorrhoidalis is always found attached to the base of a hair on 
the lips. These hairs are so small that one does not observe them 
Avith the naked eye. It is the only Gastrophilus depositing here. 
The Qgg is black in color and the stalk is partially inserted in the 
pore of the skin at the root of the hair. 

Fourth-stage lava), as can be seen in the illustration (PL I), vary 
in size when fully developed. In all specimens the eleventh ring is 
completely deprived of spines, but upon the other rings the varia- 
tions are often misleading. However, the key given herein will 
assist in identifying fully developed larvae. 

Key for the Identification of Fully Developed Lakv.e of Gastrophilus spp. 

1. Spines arranged in two alternating rows, the first more developed than the 

second 2 

Spines in one row O. nasalis. 

2. Spines long and prominent, lacking only two to three pairs on dorsal center 

of the ninth row G. intestinaUs. 

Spines short and segments prominent. Completely deprived or possessing 
only two to three pairs of spines on either side of the dorsal center of 
the ninth ring O. haemorrhoidalis. 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 



DISTRIBUTION IN THE UNITED STATES AND PROBABLE 
DISPERSION. 

Recentl}^ Mr. F. C. Bishopp, in communication with a large num- 
ber of horse breeders, has determined some facts on the distribution 
and other points, especially in regions adjoining the district where 
G. haemorrhoidalis is known to occur. This information will be 
published later. It will suffice to say here that G, JiaemorrhoidaZis 
occurs in sufficient numbers to warrant the adoption of control 
measures in the Dakotas, Montana, and northern Wyoming. Accord- 
ing to Dr. C Gordon Hewitt, Dominion Entomologist, the species 
extends over a considerable area in the Dominion of Canada. Two 
of the species, G. intesfinalis and G. n^asalis, are found throughout 
the United States where horses are present. G. pecorum is not 
knoAvn to occur in the United States. 

The constant migration of the larvse of G. haemorrhoidalis to the 
region of the anus and their dropping, which occurs over a long 
period, indicates that the principal means of dispersion is through 
the movement of infested horses. During the past few years 
large numbers of horses, which have been purchased in the 
infested district for European 
army purposes, were concentrat- 
ed at certain points until more 
could be assembled for shipment. 
This occurred at times when 
larvae were normally dropping 
and allowed ample time for this 
species to become established. 
Although the adults may not 
have appeared in sufficient nmn- 
bers to attract attention in new 
districts, this will undoubtedly 
occur in the near future. 

The comparatively short dura- 
tion of adult life and the func- 
tions of the adults restricted to 
depositing eggs indicate that 
little dispersion takes place by 
actual flight. In the nose-fly 
district there has been a slow but gradual spread of the species each 
year, as verified by hundreds of statements from farmers and horse 
breeders. 

LARVAL COLLECTIONS AND REARING TECHNIQUE. 

An insectary was located in Aberdeen, S. Dak., where all types 
of farm and city operations concerned with the use of horses could 




Fig. 3. — Gastrophilus eggss attached to hairs : 
a, G. haemorrhoiddlis and hair removed 
with root; 6, G. intcstinaU.'^ ; c, G. nasalis. 
Greatly enlarged. (Original.) 



6 BULLETIlsr 597, U. S. DEPARTMENT OF AGEICULTTJRE. 

be observed, and at the same time easily accessible to a rendering 
plant where post-mortem examinations could be made. Horses in 
pasture were available in all directions, and livery barns were located 
within a mile and could be conveniently visited. 

Horses of many types, representing every locality in the imme- 
diate vicinity, could be observed in the livery barns, and it was 
from these horses that breeding material of G. haemorrhoidalis was 
obtained. While examinations of droppings were made, most of 
the larvae utilized were removed from their places of attachment 
about the anus. These were sufficiently developed to pupate and 
produce adults, and did so even though they were not handled care- 
full}' with the forceps in removal. The number of horses in the 
liveries varied, but usually from 30 to 100 were observed daily. In 
order to obtain an ample supply of larvae additional collections were 
made when near-by farmers came in with teams. 

In rearing adults, the larvae were placed in tin boxes upon moist 
sand in California parasite-rearing boxes, or in bread trays upon 
grass sod. These were usually kept in cages 18 by 18 by 18 inches, 
each of which was fitted with a door of sufficient size to permit the 
removal of trays for examination. When adults emerged it was 
necessary to confine them in tightly fitted cages which excluded sun- 
light, and to keep them supplied with grass sod or green foliage to 
lessen activity. Sunlight has an unusually great attraction for adult 
flies. They are very active and w^ill damage their wings against 
the screen or crawl into a cage crevice and die. More especially has 
this been noted with G. haemorrhoidalis. 

LARVAL INFESTATION AND INJURIES. 
REVIEW OF OPINIONS. 

In reviewing opinions on the economic importance of bot-flies, 
one naturally encounters the ideas of Bracy Clark, which have been 
passed from one to another since 1798. He believed that larvse by 
irritating the membranes of the stomach and intestines often re- 
lieved a general disorder of the system, but mentions that, however 
useful a few of these natural stimuli may be, they result in large 
infestations which should at all times be prevented. He indicates 
in this paper that the infestations coming under his observation did 
not greatly exceed 100 larvae, and for the most part not more than 
a half dozen were to be found. 

We find the following statement by R. S. MacDougal (1899) : 

Opinion differs a good deal as to the harmfulness of these bots. In conver- 
sations with veterinary surgeons I find there is a tendency to minimize the 
evils that may attend hot presence. There are authenticated records, however, 
which place the possibility of grievous harm beyond all doubt. Inflammation, 
ulcers, interference with digestion, interference with the free passage of food 
or exit of waste matters, loss of appetite and condition, have been frequently 



GASTROPHILUS HAEMORKHOIDALIS AND OTHER BOTS. 7 

Warburton (1899) says: 

The irritation they set up can not fail, however, to be detrimental to the 
horse's health even where no ill effects are obvious. The fact seems to be that 
a horse in good condition and well fed can endure the presence of numerous 
bets in the stomach without great inconvenience, but if the animal is in poor 
condition gastric enteritis, perforation of the stomach, and death may result. 

In Miss Ormerod's report of 1890, Dr. Hy. Thompson, of Aspatria, 
Cumberland, England, says : 

I have never seen the stomacli entirely perforated, but the irritation induced 
by the development of the larva causes in many cases a great wasting of 
flesh in the horse. 

Perroncito (1902) describes lesions caused by Gastrophilus larvae, 
some of which resulted in perforation of the stomach walls and death 
of the animals. Cases of Flohill, Numan, Conti, and others, as well 
as cases coming under his personal observation, are mentioned. 

Kroning (1906) reports having observed cachexia accompanied 
with colic in young colts during the previous five years, and at- 
tributes this to infestations of bots. 

Lahille (1911) makes mention of larvse causing death of animals 
and cites the possibility of infection in the lesions. 

Yelu (1913) reports that a drought greatly favored attacks in 
Morocco and more than 1,000 larvae were usually found in post- 
mortem examinations. All three of the more common species were 
present, but G. nasalis caused lesions which resulted in death of the 
animals. 

The universal distribution of G. equi and G. nasalis has familiar- 
ized persons in every locality to some extent with bots of horses, yet 
their opinions are naturally varied as to the economic importance of 
the larvae. There are some who believe that there are no ill effects; 
others think that they are beneficial ; while some even believe that a 
horse will die if the bots are removed. Such conceptions are most 
prevalent among "horse doctors" who are not in possession of an ef- 
fective treatment for the removal of bots. On the other hand, it 
is a difficult matter to convince a horse breeder that bots are bene- 
ficial when his yearling colts kept in pastures have a rough coat, fail 
to grow or fatten, show no symptoms of disease, and at the same 
time possess a good appetite. Many breeders have made post-mortem 
examinations of horses for their personal satisfaction. The finding 
of hundreds of well developed larvae with conspicuous lesions con- 
veys vivid impressions and greatly emphasizes the importance of 
bots. Others, without a knowledge of the development of bots within 
the horse, often make examinations after numbers have been passed 
and the lesions healed ; or when the larvae are small and probably not 
observed bj^ an untrained eye they are regarded as less detrimental. 
It is only by careful post-mortem examinations of large numbers of 



8 BULLETIN 597^ U. S. DEPARTMENT OF AGRICULTUEE. 

horses that conchisions can be drawn, and these may be erroneous if 
one is not familiar with the various species, their usual points of at- 
tachment, and phenomena peculiar to each. 

SPECIES IMPLICATED. 

GastropMlis intestinalis, "the common bot," attaches ordinarily 
in the stomach, has been taken in the duodenum, but has never been 
found permanently attached in any other regions (Table I, p. 10). 
Rarely it may become temporarily attached in the rectum, but is not 
present Avith an alveolus or lesion. 

G. TiasaUs, "the throat bot," attaches by preference in the duo- 
denum, is often found in the stomach, and is the only known species 
which attaches in the pharynx. Due to the attachment in the throat, 
it not only becomes a species of vital importance when the bots 
congregate in sufficient numbers to hinder or cut off the breathing of 
the horse or cause an infection, but in this location they can not be 
removed by an internal treatment. In the duodenum the infestation 
may be sufficient to hinder or stop the passing of excreta. Table I (p. 
10) shows the comparative abundance in the stomach and duodenum 
during the period that larvas are well developed and naturally drop 
from the host. 

Various cases are on record in which this species has been removed 
from the pharynx, in all of which the authors considered it a serious 
detriment to the horse. While larvse which were not sufficiently de- 
veloped to be determined with authenticity have frequently been 
removed from the pharynx, 8 larvae of G. nasalis were collected in 
the throat of a dray horse by J. L. Webb at Reno, Nev., on August 
29, 1916. In numerous cases, both at Aberdeen, S. Dak., and at Dal- 
las, Tex., the author has found lesions present in the pharynx, indi- 
cating that the larvee had become fully developed and had passed out 
of the horse. In making post-mortem examination of horses to de- 
termine the attachment of young larva? in the pharynx extreme 
care should be exercised, as young meat-infesting larvae may be con- 
fused with Gastrophilus. Upon hatching they migrate from the 
light into the nostrils and may be found in the pharynx and other 
locations in the throat. 

Dr. BufRngton (1905), of Brooklyn, Iowa, gives a valuable history 
of a case in which a mare died as the result of an infestation of 
G. nasalis in the pharynx. This animal had experienced difficulty 
in eating for more than a month, and was unable to take food for a 
week prior to November 2G, 1903. At this time she would drink 
water, but after masticating food a very little, would drop it out. 
The symptoms were those of paralysis of the musclps of deglutition 
and there was a very offensive odor about the head. Four days later, 
when the animal died, the nasal, pharyngeal, laryngeal, and upjier 
portion of the oesophageal mucous membranes Avere found to be gan- 



Bui. 597, U. S. Dept. of Agriculture. 



Plate I. 










Stages of the Bot Flies, Gastrophilus. 

Upper Mt.— Gastrophilus hacmorrhoidalis: Female, side view. Upper right.— G. haemorrhoidalis. 
Larvje attached to margin of anus of horse. Left of center.— G. haemorrhoidalis: Last-stage 
larva. Center.— G. intestinalis: Last-stage larva. Right of center.— G. nasalis: Last-stage 
larva. Lower Mt.— G. intestinalis: Puparium,showingcapsplitofiby fly in emergence. Lower 
right.— G. haemorrhoidalis: Male, side view. (Original.) 



Bui. 597, U. S. Dept. of Agriculture. 



Plate II. 




Larv/e of the Bot Flies, Gastrophilus. 

Upper.— Attachment of last-stage larvffi and alveolar lesions upon the mucosa of the left sac 
of the stomach. Lower.-Infestation of 317 last-stage larviE, with lesions in the center. 
(Original.) 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER. BOTS. 9 

grenoiis and the source of the oifensive odor. From the pharyngeal 
walls 12 or 15 larvae were removed, 6 of which the present author 
obtained. Three of these larvae were determined as G. nasalis^ and it 
is reasonable to believe that the other larva?, which were not suffi- 
ciently developed for identification, were of the same species. 

The larvae of G. haemorrhoidaUs^ "the nose-fly," as is shown in 
Table I, may be found in the stomach, duodenum, or rectum, and 
also attached about the margin of the anus, where they change in 
color from pink to a greenish, become accustomed to the atmosphere, 
and later drop to the soil for pupation. During the early stages 
they attach within the stomach and duodenum, but later loosen them- 
selves and reattach in the rectum, from which they gradually move 
to the anus. The attacliment of clusters of these larva? in the rectum 
has been known to stop the passage of excreta and to cause abnormal 
protrusions accompanied by much suffering. 

About June 1, 1915, a horse breeder in Montana experienced a case 
of obstruction of the rectum in a yearling colt. On three different 
occasions within one week the animal was observed lying down in 
the pasture with the rectum greatly protruded. Each time it was 
washed with warm water and replaced, but the larvae causing it were 
not observed until the third time. The exact number of bots removed 
by hand was not ascertained, but upon their removal and replace- 
ment of the rectum the animal graduallj^ recovered. 

Table I records a maximum of 1,032 bots removed from a 2-year- 
old colt. The infestation consisted of 695 G. infestmalls, 248 G. 
Tiasalls, and 89 G. haetiiorrhmdalis. This was the greatest number 
obtained during any of the autopsies. Colts are always the most 
heavily infested, especially when they come from summer pastures, 
and in this case the animal was greatly emaciated, possessed a dull 
coat, and, in spite of a good appetite and an abundance of food dur- 
ing the previous winter, failed to grow or fatten. It had suffered 
from a brok«-n shoulder, the result of a kick, which ordinarily would 
have healed promptly at this age, but instead it remained for months 
a cripple. The owner, believing that it would never thrive, caused 
the animal to be killed, and the post-mortem examination revealed 
no abnormal condition, except the bot infestation and the broken 
shoulder. It appeared that so much vitality was sapped through the 
inroads of bot infestation that the colt had no recuperative surplus. 

At the date of the post-mortem examination 89 G. Jiaemorrhoidalis 
larva? had migrated to the rectum and attached. They were not suffi- 
ciently developed to pass out and were attached at this point with 
lesions characteristic of those usually found in the stomach. 

In Table I many of the infestations noted were comparatively 
small when the post-mortem examination was made, and attention 
should be called to the fact that all of these examinations were made 
11216°— 18— Bull. 597 2 



10 



BULLETIN 597, U. S. DEPARTMENT OF AGEICULTURE. 



during the time when larvae were naturally dropping with excreta. 
The numbers do not show the maximum infestations of larvae that 
may have been present. Many of the dead horses examined had 
been subjected to various environments prior to the autopsies and are 
not representative of infestations found when horses have spent the 
entire previous summer in pastures. 



Table I. 



-Gastrophilus findings in post-mortem examinations of horses at Aher- 
deen, S. Dak., 1915-16. 





Spent summer. 


Larvae in stomach. 


Larvae in duodenum. 


d 
» 2 

■1 

1-^ 


a 

1 



Horse 
died. 


.23 

"a 
a 

a 

a 

6 


.a 

d 


'0 

Km . 

11 

Xi 

6 


If 



.23 

"3 

.a 

1 
.g 

6 


a 

6 


'0 

u 

Xi 

6 


3 

03 " 




1915. 




295 

158 

103 

68 

33 

18 

6 


11 
'296' 


21 
12 

1 
3 












9 
14 


1 337 


July 8 
July 14 
July 21 
July 26 
Aug. 12 
Aug. 23 
Aug. 23 
Aug. 26 
Aug. 26 
Aug. 26 
Sept. 13 
Sept. 17 
Sept. 20 
Sept. 21 
Oct 1 














184 






11 


1 






116 










351 


Driven on streets 












1 


34 


. do 










1 




18 


do 






10 
67 
35 
71 
42 
217 
101 












16 


In pasture, 1915 
















67 




9 
5 


1 














45 














76 


















42 


Country and town driving . . 


















217 
















71 
22 
13 

82 




172 
















22 


do 


1 
6 

123 
7 
56 
44 
64 
18 
16 
3 

687 
72 

116 
92 

461 

151 
39 
20 






4 
50 








18 


Farm work 












138 


1916. 
May 20 
May 20 
May 29 
May 29 


. . do 


15 


7 








145 
















7 




1 
10 


10 
35 














67 








22 

6 
19 








111 








2 






71 








5 
1 










42 


June 16 














17 


June 21 


Driven on streets 














3 


June 26 




70 
2 
2 

5 






7 


178 
137 
19 
144 
149 






89 


2 1,032 


June 28 


do . 


26 








237 


July 11 
July 17 
July 24 
Aug. 3 
Aug. 4 
Aug. 7 
Aug, 6 
Aug. 11 
Aug. 11 
Aug. 23 
Aug. 23 
Aug. 26 
Sept. 1 
Sept. 8 
Sept. 11 
Sept. 16 


Farm work 


_ 




1 






138 


do 










241 














610 


Farm work 


1 
16 


1 

4 












153 






4 


30 
25 

1 








93 




2 






47 








13 








14 




24 

29 

1 

44 

23 

1 

2 

5 

2 












24 




14 


1 






4 








48 




6 

8 






26 
16 
12 




33 






8 




26 
1 




102 




36 








20 

1 




21 






1 








14 




18 




1 






6 








37 






31 




70 

















1 Includes 1 G. intestinaUs temporarily attached in colon. 

2 Includes 1 G. intestinaUs temporarily attached in rectum. 

LARVAL MOVEMENTS WITHIN THE HORSE. 

When a post-mortem examination is made, the larvae usually are 
found quiescent, although occasionally some may be observed to move 
the posterior end slightly. The smaller larvae show more activity 
than do well-developed ones. 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 11 

Other than G. nasalis^ which sometimes attaches in the pharynx, 
the first-stage hirva? attach to various portions of the stomach and 
duodenum. In the stomach young larvae have been removed from 
various locations, including both the cardiac and pyloric portions. 
The last-stage larvae of all three species are found in the various por- 
tions. Gastrophilus intestinalis is confined for the most part to the 
mucosa of the left sac, though this species has been taken in the 
right sac and in the duodenum (see Table I). In the early stages 
some of the larvae either change places of attachment or pass out of 
the horse undeveloped. With last-stage larva^ the indications are 
that, excepting G. haeTnon'hoidalis, they remain attached at one 
place continuously during feeding, as in early spring the number of 
larvae and lesions upon the mucosa is the same. 

During the early spring or perhaps even in winter the larvae of 
G. Juiemorrhoidalis move from the stomach and duodenum to the 
rectum where they may be found permanently attached in clusters. 
It is evident that they feed in this position, as lesions are sometimes 
present. Later when they move to the margin of the anus no lesions 
are present and apparently the larvae only pause to become accustomed 
to air temperatures before dropping. 

There is no definitely periodic larval migration of G. haemorrhoi- 
dalis, as some last-stage larvae are found in the stomach and duode- 
num until early fall. Through the courtesy of Dr. L. Van Es, of the 
North Dakota Experiment Station, some post-mortem examinations 
were made at Fargo, N. Dak., and larvae preserved according to 
their location within the animal. During the winter these larvae 
were found in the stomach, and on July 10, 1916, 3 larva?; July 11, 
1916, 16 larvae; and August 18, 1916, 2 larvae were fully developed 
and in the same regions. This coincides with the findings at Aber- 
deen, S. Dak., although one last-stage larva was found in the stomach 
on September 8, 1916. 

POINTS OF LARVAL ATTACHMENT. 

When an opened stomach of a horse is examined, one is impressed 
by the contrast in the left and right portions. Around the entire 
organ a line of demarcation is represented by a prominent sinuous 
crest. In the left portion, which is often called the left sac, the 
mucosa is white, dry, resistant, and covered by a thick layer of 
epithelium. This covering is identical with that of the esophagus 
and may be considered as a widening of the esophageal canal. 

Dr. Guyot, in describing the mucosa of the left sac, says the struc- 
ture is analogous to that of the skin. It is dermo-papillary, with 
epithelium of the Malpighian type, but possesses a muscle, the 
Tmtscularis rriMcosae^ which is peculiar to it. The structure of the 



12 BULLETIN 501, U. S. DEEAKTMENT OF AGKICULTURE. 

right sac differs in having a soft membrane with an epithelium 
formed by a single hiyer of cells. 

G. intestinalis larvae are practically always fonnd attached in the 
left sac, and it is the opinion of Dr. Gnyot that this portion affords 
the most stable point for larval attachment. He thinks that cases 
are exceptional in which larvse maintain themselves in the right sac. 
This, however, does not explain the attachment of G. na-saJis in the 
duodenum and to the walls of the pharynx, nor does it account for 
the attachment of G. haemon^hoidalis in the right sac of the stomach, 
in the duodenum, or in the rectum. As has been mentioned by 
Dr. Guyot, the reason for attachment in certain regions of the diges- 
tive tract will remain a mystery until the manner in which larva3 
are nourished is ascertained. 

Various investigators have been unable to discover white or red 
corpuscles of the horse in the pharynx and other alimentary portions 
of the larva3. Clark believed their food was probably the chyle, but 
Guyot rejects this explanation, as larvae in the pharynx are located 
where this could not possibly be utilized. As Oestrus ovis larvae 
nourish themselves with the mucus secreted by the mucosa of the 
nose and frontal sinuses of sheep, and as those of Hypoderma utilize 
the pus of the abscesses which they create by their presence in cattle, 
he believes it permissible to suppose that those of Gastrophilus find 
nutriment in the inflammatory products of the gastric mucosa. 

It w^ould appear, from observations, that Gastrophilus larva3 some- 
times feed upon the blood of the animal, although they are not de- 
pendent upon it for subsistence. The red and maroon color of G. 
intestinalis and G. hcemorrhoidalis, with their attachment upon 
points other than the mucosa of the left sac, would bear out this 
hypothesis, which is further supported by the fact that G. haenfior- 
r/ioidaHs when fully developed in the rectum still retains a pinkish 
color. 

THE ALVEOLAR LESIONS OF THE STOMACH. 

In Dr. Guyot's examinations of lesions caused by the attachment 
of larva3 to the mucosa of the left sac, the muscular coat was not 
damaged. The condition found was merely a localized inflammation 
around the point of larval attachment, in which the derma had been 
invaded by leucocytes. He assumes that this is only the common 
inflammatory reaction which would be normally produced around 
any foreign body. 

In following these studies Perroncito found that the bottom of the 
alveolus varied in size and became the seat of a more or less remark- 
able inflammatory process. This produced a thickening of the walls 
of the stomach and finally the disappearance of the muscular tissue, 
which becomes hard and compact, preventing the normal functions of 



GASTROPHILUS HAEMOREHOIDALIS AND OTHER BOTS. 13 

the stomach. He mentions cases of perforations, lacerations, and 
rnpturcs of the stomach observed by Flohill, Nnman, Conti, and 
Brusasco, and calls attention to alveolar lesions which are natnrally 
more predisposed to induce various infective diseases. (See Plate II.) 

GASTROPHILUS AND SWAMP FEVER. 

Aside from the lesions Avhich may induce the entrance of organisms 
of infectious diseases, the Seyderhelms, of Strassburg (1014), report 
results which they think implicate Gastrophilus larvfe in the causa- 
tion of swamp fever. It is believed by them that the larvw excrete 
a specific toxin which is the cause of the disease, for by administer- 
ing extracts of these larva? symptoms typical of swamp fever have 
been observed. The coincidental distribution of Gastrophilus with 
that of this disease would appear to bear out the hypothesis. It is 
said that the most virulent reactions were obtained in these experi- 
ments with G. haemorrhoidalh larvae. 

BOT-FLY ANNOYANCE. 

In those portions of the country where the nose-fly does not occur, 
horses are seldom sufficiently annoyed to require protection. The 
persistence of the common bot-fly and the repeated stamping of the 
animals are evidence that it is annoying, but when the throat bot- 
fly " strikes " the action of the horse becomes more violent. 

The throat bot-flj^ is less persistent but more determined in de- 
positing, and the horse usually responds with a violent nod or jerk, 
the violence depending upon the nervousness of the individual. In 
plowing it is sometimes necessary to place a strip of cloth or a small 
brancli of a tree underneath the throat latch and extending to the bit 
rings. 

In the nose-fly section the annoyance is produced by the two gener- 
ally distributed species in addition to G. haeTrwrrhoidalis. Upon the 
approach of this fly the horse moves the head backward and forward 
to prevent its darting on the lips, but this only seems to arouse its 
determination, for it quickly alights on the lips and witliin a second 
or two deposits a black egg. It apparently occasions a most annoy- 
ing sensation, and a horse will most often snort and rub violently 
against the ground, a bowdder, a tree, barb-wire fence, or any con- 
venient object. 

The effects of ovipositions on pastured animals are worry, loss of 
flesh, and mechanical injuries. If the lips are examined barb-wire 
lesions will be found AVJiich resulted from the rubbing of the horse 
following an oviposition. (See Plate IV.) 

With an unprotected work animal one may be suddenly confronted 
with a jerk or a similar violent action of the animal at each oviposi- 
tion of the fly. When a few eggs have been deposited the animal 



14 BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 

proceeds from infuriated shaking of the head, sometimes accompanied 
by loud snorts, to complete loss of self-control, and will use any 
means for self-protection. Numerous runaways naturally occur and 
serious accidents have also occurred when horses were being used 
for mowing. The majorit}^ of farmers and breeders contend that 
" the fly stings the horse in the nose." The reactions of the animals 
are often so violent that at first it seemed that the horses really 
experienced pain. Dr. Parker, of the Montana State Board of 
Entomology, has published some notes ^ to the effect that the eggs 
were thrust into the skin, but he failed to recognize the minute hairs 
to which the eggs are attached. The poini jd portion of the egg is 
merely a device by which it is attached to the hair. A horse does 
not experience any pain, as the ovipositions do not puncture the skin. 
Neither do the flies deposit in the nostrils. Careful search has 
failed to disclose a single egg in such locations, and it would appear 
that the snorting of the animal has given rise to this " popular 
opinion." It is believed, however, that annoyance is largel}" due at 
first to an instinctive fear and later to a tickling sensation when the 
eggs are attached to the minute hairs, as the lips are the most sensi- 
tive portions of the horse. Prr.ctically all horses in this section have 
sore lips from eating a " wild barley " or " foxtail grass " {Hordeum 
jvhatum) and there is no doubt that this soreness contributes to 
the annoyance. 

NATURAL PROTECTION OF HORSES. 

The flies show no preference as to type, breed, color, or age, but 
naturally oviposit upon unprotected animals. Horses seek protection 
in pastures, the individuals gathering in a bunch and resting their 
lips upon one another. Colts and young animals not high enough 
to protect their lips in this wa}^ receive an abundance of eggs. 

A horse will sometimes hold the lips upon the ground as if grazing, 
upon detecting the presence of the fly, and when held in such posi- 
tion the adult fly is rarely observed to oviposit. Often the annoyance 
of biting flies and other depositing Gastrophilus will cause a horse 
to walk, holding the lips near the ground. Frequently other horses 
will follow and protect themselves by placing their lips upon his 
back or the backs of other animals in the line. Usually they search 
for the highest elevation where the breeze is blowing, or for standing 
water, but if an open stall is convenient they will use it to good 
advantage. If protection is not found an unconfined animal will 
often wander a great distance from home. 

Upon a bright still day ovipositions occur from 8 a. m. until about 
sunset, and the group of horses may be observed to shift from place 

^ See " Bibliographj-," page 50. 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 15 

to place without eating, their lips resting upon one another, or they 
may congregate with cattle, which are not subject to attack. The 
horses spend such days in awaiting darkness, after which feeding 
takes place. Characteristic positions of the animals are shown in 
Plate III. 

Wind with a velocity of 15 miles an hour or more greatly relieves 
the animals, and persons driving horses about thrashing machines 
often stop them so that they face the breeze. 

Cloudiness is also a protection to horses, and if only a light cloud 
conceals the sun a bunch of horses may be observed to disperse and 
begin grazing. Often their feeding will have only begun when the 
sunlight returns, causing them again to seek protection in a group. 

Horses in standing water are not annoyed b}^ nose flies and fre- 
quently they seek this protection in order to eat, despite the fact 
that hundreds of mosquitoes feed upon each animal. This standing 
or feeding upon grass in water is excellent for a foundered horse, 
and the mud which adheres to his legs prevents G. intestinalls from 
ovipositing upon them. 

While the wind and cloudiness are especially protective against 
G. haemorrhoidalis^ the other two species of bot-flies are not much 
affected thereby. G. hitestinalis may be observed to oviposit on 
windy and cloudy days. G. nasalis deposits under more adverse 
conditions than does G. haeTnorrhoidalis^ but seems to be more sensi- 
tive to natural agencies than is G. intestinalls. 

In barns the species of Gastrophilus never have been observed to 
oviposit. On numerous occasions ovipositing adults have been ob- 
served to pursue the animal only until it reaches the stall door. 
Post-mortem examinations of horses which had been confined in 
stalls failed to reveal a single larva. One of our correspondents 
reports that the annoyance of G. Jiaemorrhaidalis was greatly re- 
duced when he constructed a simple shed in the pasture where the 
horses could congregate. 

SEASONAL HISTORY OF GASTROPHILUS. 

At Aberdeen, S. Dak., the larvse of G. haemorrhoidcdis are ob- 
served attached to the margin of the anus of horses as early as May 
5 to 10, and if suitable temperatures occur adults may be expected a 
little prior to June 15. 

From June 21 to 27, 1915, G. haemorrTwidalh adults appeared at 
Lodge Grass, Hardin, Billings, Miles City, and Custer, Mont. At 
the same time they appeared at Aberdeen, S. Dak., and neighboring 
points. They have been observed at Aberdeen, S. Dak., as late as 
October 10, though they are seldom found after a killing frost, which 
is usually about September 15. 



16 BULLETIN 597, U. S. DEPAETMENT OF AGKICULTUEE. 

The other two species appear at Aberdeen, S. Dak., about the same 
time as G. hae7non^holdalis^ but are most abundant just before a 
killing frost. The G. haemorrhoidalis are least abundant at this 
time, and are present in greater numbers during the early half of the 
season. After a killing fi'ost one seldom finds a Gastrophilus except 
when warm temperatures prevail during a few days. 

In the " nose-fly " district one must bear in mind that the period 
during which flies oviposit is that when farmers are most busy, and 
the most favorable time for fly ovipositions is when the weather is 
most favorable for working horses. The adults appear during the 
plowing of corn and sorghum, and the annoyance continues during 
the mowing of hay, the harvesting and thrashing of grain, and the 
marketing of farm products. 

GASTROPHILUS HAEMORRHOIDALIS (Linnaeus). 

SYNONYMY. 

Ocstriis JiaemorrJioidalis Linnaeus, 1761. 
Gnstrophiliis haemorrhoidalis Leach, 1817. 
Gastrus haemorrhoidalis Meigen, 1824. 

ATTACHMENT IN RECTUM AND DROPPING OF LARV^. 

During the early spring and summer the fourth-stage larvae are 
normally concealed within the rectum, where lesions have been noted 
in post-mortem examinations. Later they effect a temporary attach- 
ment to the margin of the anus, where they become accustomed to the 
air temperatures, assume a greenish color, and apparently increase 
their motility. Larvae, normally exposed to the air at the rectum, 
after dropping seem to conceal themselves at grass roots so as to be 
protected from the heat of the sun much more easily than those 
unexposed at the margin of the anus. When a larva is attached 
so that only the posterior end is exposed at the rectum one will find 
the anterior end a pinkish color, while the posterior will be greenish. 

Larvae exposed at the rectum have been observed for the length of 
time they remain attached, and the shortest period was slightly more 
than 40 hours, while the longest was 71 hours. The heat of the sun 
for a few minutes was sufficient to cause larvae to drop when an 
attempt was made to photograph a larval attachment at the anus. 
At various times during the day larvae appear at the anus, as many 
as 13 sometimes being visible at one time. The larvae are likely to 
drop under most any condition, but do not drop with manure, as is 
supposed. When manure is dropped during their attachment they 
seem to use more effort in clinging and are only pushed aside during 
its passage. (See Plate I, figure at upper right.) 

PREPIJPATION AND PUPAL PERIODS. 

In the normal pupation of a larva which has been exposed at the 
margin of the anus there is a gradual change from greenish to yel- 



Bui. 597, U. S. Dept. of Agriculture. 



Plate III. 




Protection from Bot Flies. 

Upper.— Horses assembled for protection during ovipositions of Gastrophilus hacmorrhoidalis. 
Center.— A method of protecting lips from ovipositing G. hacmorrhoidalis. Lower.— Protect- 
ing under jaws from ovipositing G. nasalis. (Original.) 



Bui. 597, U. S. Dept. of Agriculture. 



Plate IV. 




Secondary Injury from Bot Flies. 

Upper. — Horses rubbing following ovipositions of Gaatrophilus haemorrhoidalis. Lower. — Lower 
lip of horse showing barbed wire cut at the lower extremity which resulted from rubbing. 
The small holes are injury from the grass Hordeum juhatum. (Original.) 



GASTROPHILUS HAEMOEKHOIDALIS AND OTHER BOTS. 



17 



lowish, the larva contracting and assuming the form of a pupa. As 
the puparium becomes more hardened a reddish tinge appears, but 
after a few days it becomes black and retains this color until the 
adult emerges. 



Table II. 



'Some environmental effects on metamorphosis of Gastrophilus 
haemorrhoidaUs at Aberdeen, 8. Dak. 



Larvse 
collected 

from 
rectum. 



Environment. 



Pre- 
pupal 
period. 



Pupal 
period. 



Temperature, col- 
lection to emer- 
gence. 



Max. 



Min. 



Mean. 



Num- 


Num- 


ber 


ber 


lar- 


pu- 


vae. 


pae. 


14 


14 


33 


31 


16 


13 


7 


7 


12 


11 


14 


14 


10 


10 


10 


8 


7 


6 


27 


25 


34 


30 


33 


33 


H 


5 


7 


7 


5 


4 





4 


2 


2 


1 


1 


11 


8 


17 


17 


28 


25 


46 


44 



Number 

adults 

emerged. 



Lon- 
gevi- 
ty 
of 
larvae 
not 
pu- 
pat- 
ing. 



1915. 
June 4 
Jime 5 
June 7 
June 8 
June 9 
June 12 

June 15 
Do... 
Do... 
June 14 
Jime 18 
June 17 
July 12 
Aug. 7 

1916. 
May 22 
May 23 
May 30 
May 31 
June 3 
June 5 
June 10 
June 23 



Fresh horse manure in tin box 
■ do 
da 
da 



Clean tin box 

Glass jar and fresh horse ma- 
nure 

Dry hard soil 

Moist horse manure 

Clean tin box 

do 

do 

Moist manure in tin box 

Black loam in tin can 

On grass sod 



Hours. 
27-47 
24-72 
34-52 
49 
35-55 

53-146 

75-122 

122 

120 

50-144 

27 

18-47 

23-39 

19-26 



Clean tin box 

do 52-72 

do 141-170 

do : 

do I 42-96 

With moist sand \ 75-100 

do , 44 

Clean tin box and moist loam. 



Days. 
39-45 
46-54 
37-44 
38-40 
36-48 

33-36 
28-30 
29-31 
31-32 
30-38 
32-42 
34-40 
34-35 
58-68 



41 
36-40 
34-35 

35 
33-34 
32-35 
30-32 
21-24 



F. 



" F. 
35 
35 
35 
35 
35 

40 
40 
40 
40 
40 
40 
40 
40 
132 



" F. 
63.21 

64.76 
64.93 
65.67 
65.02 

65.73 
62.40 
62.56 
62.89 
64.33 
63.23 
62.06 
64.23 
60.59 



62.62 
62.81 
64.79 
60.08 
65.55 
66.69 
68.15 
74.08 



Days. 



15-22 
15 
16 
12 



1 Minimum, Sept. 21. 

In rearing larA'se to adults a most convenient and efficient method 
was utilized by placing them in clean tin salve boxes upon moist sand 
in bread pans. Table II gives some results of rearing under such 
conditions, using various media within the tin boxes. The period of 
collections extends from June 4 to August 7, which includes prac- 
tically the entire season during which larvcT appear at the anus of 
horses in Aberdeen, S. Dak. It Avill be observed that the prepupal 
stage, the period from removal of larvpe until pupation, varies from 
18 to 170 hours. This is a much greater range of time than is normal 
and may be attributed to the fact that larvse were removed before the 
critical period of dropping. In some instances under varying con- 
ditions they did not pupate, and, while some larvse died within a few 
days, one is recorded as living, for 22 days. 

The removal of larvse from the rectum prior to their normal ex- 
posure to the air at the margin of the anus has a pronounced effect 
upon rearing. A small percentage have been reared which were fully 
11216°— 18— Bull. 597 3 



18 BULLETIN" 597, U. S. DEPARTMENT OF AGRICULTUEE. 

developed and concealed within the rectum, but larvae less than 
normal size, which were not exposed at the margin of the anus, did 
not produce adults. Only larvae possessing the greenish color indi- 
cating exposure at the margin of the anus were used in experiments 
recorded in the tables. 

In Table II, of 347 larvae collected, 319 pupated and produced 236 
adults, the pupa period varying from 21 to 68 days. The" greater 
portion emerged during the shorter periods indicated in the table. 

FATE OF LARV^ DROPPING UNDER VARYING CONDITIONS. 

The variety of conditions under which larvae are dropped naturally 
suggests the question of their ultimate fate. In an effort to deter- 
mine this point by experiments, the most striking phenomenon ob- 
served was the larval " migration " which precedes pupation. In ex- 
periments recorded in Table III, larvae placed upon the surface of 
the soil or media penetrated to a slight depth for protection of the 
pupge. With larvae buried in loose soil, as would ordinarily occur 
when they are dropped by plow horses, they moved upward to near 
the surface for pupation. 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 



19 



1 




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20 BULLETIN 597, U. S. DEPARTMENT OF AGEICULTURE. 

Questioning the fate of pupae if buried, a lot consisting of larvse 
that had moved near to the surface before pupating were replaced in 
moist loam to a depth of 5 inches. The adults had no difficulty 
in penetrating this soil, as 29 emerged normally from 32 pupae. 
A lot of 15 larvse buried 4 inches under black loam and fresh horse 
manure produced 14 pupse, many of which were located near the 
surface. Lachnosterna larvse were present and during their develop- 
ment kept the soil well pulverized. Of the 14 pupse, 8 produced 
normal adults. 

The experiments cited in Table III, with the exception of the 
lot of puparia eaten by a field mouse, show that the greater emer- 
gence percentage occurred when larvse were placed upon grass sod. 
By this method sufficient moisture was supplied, and at the same time 
the movement of the larvse to the roots of the grass protected the 
pupse from excessive heat. In one lot 32 adults emerged from 35 
pupse, and in another, under similar conditions, 38 adults emerged 
from 42 pupse. 

It is also noted from other experiments that excessive moisture 
or dryness is less favorable for the metamorphosis. 

EFFECT OF HEAT ON LARV^ AND PUP^. 

Doubtless numerous larvse and pupse are subjected to heat, in 
barren places, when dropping from work horses driven upon the 
roads. This may not be confined to the heat of the sun, for horses 
standing in stalls may drop larvse which are placed with the manure 
in piles that generate heat. The results of some tests are given in 
Table IV. 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 



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22 



BULLETIN 597, U. S. DEPABTMENT OF AGBICULTTJRE. 



Upon hard soil the larvae are seldom observed to move more than 
a foot, and this sometimes requires 15 minutes. The tendency seems 
to be confined almost wholly to burrowing, and it is only when 
dropped on unsuitable places that they migrate. When exposed 
upon hard, barren soil to the heat of the sun during the summer it- 
seems certain that only a few find protection and eventually produce 
adults. Certainly those not finding suitable protection from the sun's 
heat die within a short time. On black loam at a mean temperature 
of 122.9° F., 8 to 12 minute exposures caused 100 per cent mortality. 
Yet some larvae seem to withstand even higher temperatures, for 
adults were produced after having been exposed from 5 to 17 minutes 
at a mean of 129° F. Pupae, being unable to accommodate themselves 
by moving for protection, seem to be very susceptible to heat. Ex- 
posures of from 30 to 137 minutes at 116.6° F. were sufficient to 
render them inviable. 

The heat generated in a manure pile produced greater mortality 
upon larvae than ordinarily would be expected. Larvae buried with- 
out protection at a mean temperature of 151.7° F. were dead within 
15 minutes, having become soft and white. 

EFFECT OF SUBMERGENCE ON LARV.^ AND PUP^. 

Although, as shown in Table III, excess moisture seems to have 
had a destructive effect upon pupa?, the effect of submergence upon 
larvae is not so great. Larvae submerged 51 to 74 hours pupated and 
produced adults. (See Table V.) Larvae submerged for 80 hours 
pupated, but failed to emerge when kept under favorable breeding 
conditions. While it is difficult to submerge pupae, as they float and 
expose a portion of the posterior spiracles, three normal ones kept in 
water for 5 days failed to emerge. In view of the results in Table 
III, it is apparent that great mortality occurs among pupae during 
wet seasons. 

Table V. — Effect of submergence on larvw and pupce of Gastrophilus haenior- 
rhoidaUs at Aberdeen, -S. Dak., 1!)15—16. 



Date 


Stage. 


Num- 
ber. 


Period 
submerged. 


Num- 
ber 

pupat- 
ed. 


Adults 
emerged, 
(male.) 


Larval 

lon- 
gevity, 
includ- 
ing 
period 
of sub- 
mer- 
gence. 


Collec- 
tion to 
emer- 
gence. 


Temperature after 

period of 

submergence. 


merged. 


Max. 


Min. 


Mean. 


1915. 
July 5.. 


Larvae... 

do 

do 

do.... 

Pupae... 

Larvae., 
do.... 
do.... 
do.... 
do.... 


6 
3 
3 
5 
3 

9 
5 
15 

5 
5 


51 hours 


4 
2 






1 


3 
1 


Days. 
5 

"17-26" 
9-14 


Days. 
36 
38 


op 

85 
85 
85 
80 
82 

76 
76 
96 
96 
96 


"F. 
41 
41 
41 
40 
40 

43 
43 
64 
64 
64 


"F. 
63.93 


July 14. . 


74 hours 


64.21 


Do... 


20 days... . 


62. 9S 


July 24. . 


14 days 




58. 14 


July 2.. 


5 days 




59.40 


1916. 
June 7.. 


7 days 




12 
8-12 

8 
4 

7 




64.83 


Do... 


6 days 




64.83 


July 12.. 


7} days 




76.50 


Do... 


80 hours 


5 




75.90 


Do... 


5i days 




76.50 













GASTKOPHILUS HAEMOEKHOIDALIS AND OTHEE BOTS. 23 

LarA^se have been observed to remain alive during submergence for 
from 14 to 20 days ; those submerged 6 and 7 days live for some few 
days after removal. 

NATURAL CONTROL. 

FUNGUS DEVELOPMENT. 

Under conditions the same as those upon which adults were reared 
in Table II apparently two species of fungi developed upon living 
material. The first mentioned in Table VI occurred upon three larvae, 
to one of which a particle of horse manure adhered. They were 
collected from the rectum of perspiring horses, and it appeared that 
the fungus developed from the manure and spread to the larvse and 
pupse. The larvse giving promise of fungus development were 
placed in a clean tin pill box with three well-washed G. haemor- 
rKoidalis larvae, which had been exposed to the air at the anus of a 
horse for about 24 hours preceding the washing. The fungus de- 
veloped upon all the larvae and death ensued. This fungus was 
determined by Mrs. Flora W. Patterson, Mycologist of the Bureau 
of Plant Industry, as Sporotrichunh minutum. This, with one ex- 
ception, was the only lot in which fungi appeared on living larvae. 
As this fungus had developed upon larvae collected from perspiring 
horses, it seemed possible that such larvae as were not washed might 
have developed a superficial growth. Later collections were made 
from work animals which were perspiring during the time of collec- 
tion, and they were kept under similar conditions, but no fungus ap- 
peared. In collections of larvae kept under normal rearing condi- 
tions, as given in Table VI, a fungus appeared on the pupa stages 
which apparently spread to other pupae in the same lot. In some lots 
pupae remained without becoming infected, but in others it even 
developed upon various parts of the tin boxes. The collections and 
rearing methods used in these experiments were not unlike those in 
which no fungus appeared, as new, clean, but unsterilized tin boxes 
were used in each breeding experiment, and sterilized forceps were 
used in handling. The soil or medium was different in the various 
boxes, but since these various conditions were also present in lots 
which developed no fungi, there appears to be no reason for attrib- 
uting it to the type of soil or to the medium. Upon the pupae it 
appeared within from 3 to 17 days after collection. 



24 



BULLETIN 597, U. S. DEPAETMENT OF AGRICULTURE. 



Table VI. — Fungtis development upon pupw of Gastrophilus haemorrhoidalis 
in new tin boives at Aberdeen, S. Dak., 1915-16. 



Larvae 

from 

rectum. 


Collection and environment. 


1 

! 

S" 
& 
o 
u 


a> 
C3 

& 
ft 
C8 

1 


•6 

K 
t 

3 
fin 


'6 


1 

ffi 


•6 

C3 
ft 

t 


Number 
infected. 


Adults 
emerged 


Temperature 
collection to 
emergence. 


ft 

3 


1 


<6 
1 


_2 

a 

IS 


X 


.s 


1 


1915. 
June 111 
June 15 


From perspiring horses 


Hows. 
79-220 
75 
20-219 
6-25 
23 
6-43 
5-18 
21-29 

22-32 
20-39 
77-102 
48-72 
22-70 
4-122 
19-166 
22-190 
3-64 
21-67 
21-31 


1915. 
June 15 
June 30 
June 25 
July 13 


Days. 
34-36 
35-38 
30-32 
34 


13 

10 

34 

5 

1 

3 

40 

4 

7 
13 

2 

8 
10 
62 
20 
15 

4 
14 
19 


10 

10 

29 

3 

1 

3 

40 

4 

7 
11 

2 

7 

10 
59 
17 
13 

4 
12 
18 


10 
10 
29 
3 

3 
40 
4 

7 
11 
2 
7 

10 
59 
16 
12 
4 
2 
18 


3 
"5' 


2 
5 

7 

1 


2 
1 
6 


"F. 

88 
88 
85 
85 


"F. 
40 
40 
41 
41 


"F. 
65.54 
64 66 


June 21 




63 88 


July 6 


With fresh horse manure . . 
From perspiring horse 


6 J. 85 


July 7 
July 10 


July 13 

...do 

July 16 

1916. 
May 29 
June 14 
June 22 
June 12 
June 17 
June 29 
July 1 
July 3 
July 6 
July 25 
July 28 


33-36 
33-36 
33-35 

'21-25" 

'21-29' 
20 

""29' 




1 
14 

1 


1 
11 

1 


85 
85 
85 


41 
41 
41 


62 12 


With moist loam 


64 32 


July 13 




64 43 


1916. 
May 17 2 


On blotting paper 




June 2 2 
















June 5 




.... 







76 


42 


59 14 


Do.2.. 


With moist sand 




June 9 2 


do 














June 24 


do 




24 


15 


96 


48 


74 67 


June 262 






June 27 






4 




96 
96 


56 

58 


75 73 


July 1 




77.07 


July 182 


Witli moist sand 








July 24 






5 


3 


98 


51 


70.19 









1 Determined by Mrs. Flora W. Patterson as Sporotrichum minutum. 

2 Determined by Dr. A. T. Speare. 

Except the collection on May 17, 1916, larva? were not washed. 

Several lots Avere sent to Dr. A. T. Speare, Mycoentomologist of 
the Bureau of Entomology, who made cultures and determined the 
characters showing that all the infestations w^re of one species and 
were not Sporotrichum. 

According to Dr. Speare about 50 per cent of the pupse sent to him 
produced adults. He reported that the fungus seemed to be restricted 
in its development to the chitinous wall of the puparium, and that 
death, if caused by the fungus, must have been brought about in some 
unusual Avay, as, for example, by closing the spiracles. However, 
the fungus seems to develop best at the rings of the segments and is 
seldom observed upon the posterior spiracles. 

In Table IV it will be observed that a fungus appeared upon pupae 
which had been subjected to heat tests, and this was apparently the 
same as has been observed in other experiments. A comparison of 
results and mortalities due to the fungi indicates that there is little 
hope of controlling the Gastrophilus by encouraging natural develop- 
ment of the fungus. Eighteen lots containing 283 larva^ produced 259 
pupae, of which 247 became infected with fungus in rearing experi- 
ments. Twelve of the lots, containing 194 pupae, were retained for 
observations on mortality. Of these, 64 males and 47 females 
emerged as normal adults, giving 57 per cent emergence. The adults 



GASTROPHILUS HAEMORRHOIDALIS AXD OTHER BOTS. 25 

possessed a normal longeAit}^ as compared with others in rearing 
experiments. 

The above percentage of mortality is based upon those experiments 
in which the fungus occurred. As there seems to be no reason for 
attributing the fungus to soil or media it is well to base this per- 
centage upon all experiments in tin boxes and where pupae were in 
close proximit^^ In Tables II and VI, 630 larvse produced 578 pupte. 
Of these 247, or approximatel}'^ 43 per cent, dcA^eloped a fungus. Of 
the ones kept under observation 57 per cent emerged, so that only 43 
per cent of the infected pup?e were rendered inviable; 43 per cent 
of 43 per cent would approximate 18.5 per cent, or the percentage of 
loss in rearing experiments where numbers were kept in close prox- 
imity, which probabl}^ allowed the infection to spread over indi- 
vidual lots. 

In Table III it is shown that no infected pupse were found, and 
should a fungus develop in such conditions the single location of 
pupae would prevent its spreading. This fungus has never been ob- 
served upon normal G. intestinalis or G. nasalis^ though with dead 
larva? of any Gastrophilus a long growth of fungus quite different 
from that met upon living G. haemonhoidalls pupa? is frequently 
found. 

PREDATORS AXD PARASITES. 

The dropping of larvae under varying conditions and in locations 
where the^^ do not pupate in close proximity renders the situation 
such that A'er}' little could be expected of predators and parasites in 
control. In rearing experiments some field mice devoured pupae 
on grass sod, but even though they feed upon these in nature it 
is not likely that a great many are devoured. Chickens probably do 
not feed upon many larvae when they drop, though a single hen has 
been known to devour about 40 dead G. intestinalis removed from a 
horse by a carbon disulphid treatment, and without any noticeable ill 
effects upon the chicken. 

Desiring to know if the widely distributed Nasonia hrevicorms^ 
which parasitizes various species of dipterous pupae, could be reared 
upon G. haemorrhoidalis pupae, repeated efforts were made, but with- 
out success. The indications are that the flycatchers feed very little 
upon Gastrophilus adults. On account of the danger in shooting 
such birds in pastures very few examinations of stomachs have been 
made. 

LIFE-HISTORY NOTES- 
ADULT LONGEVITY. 

The life of adults appeared so short at the beginning of experi- 
ments that it W' as attributed to abnormal conditions, but various cages 
and environments did not materiallv increase the periods. A total of 
11216°— IS— Bull. 597 4 



26 BULLETIN 597, U. S. DEPARTMEXT OF AGKICULTUKE. 

254 males and 184 females were used in the experiments. All of 
these emerged normally from reared material. While some adults 
died on the first and second days the maximum longevity was 7 days. 
The greater periods were always obtained when the cages were kept 
out of the bright sunlight and provided with more or less foliage to 
prevent adults from battering themselves against the sides of the 
cage. Twenty-seven males and 15 females liberated in the insectary 
(9 by 12 by 7 feet) died within 1 to 3 days and were found dead 
at a sunny exposure with the wings battered. Cages admitting a 
great amount of light and without foliage yielded similar periods of 
longevity. 

Adults in screen cages 18 by 18 by 18 inches or in a parasite- 
rearing box (covered on two sides with glass and arm holes in the 
ends) usually died within 3 days. This longevity was slightly ex- 
tended when green twigs were frequently replenished. 

The longest periods were obtained in Avooden boxes 4 by 4 by 6 
inches half filled with moist soil and provided with a green twig 
and a glass cover. This lessened adult activity, and from the 51 
longevity experiments it was observed that the greater periods were 
alwa3^s accompanied with the least activity, while the converse was 
also true. These wooden boxes placed in the shade admitted enough 
light to permit of activity and flies were often observed to fly about 
with the head near the glass and would alight on the green twigs 
and rest. The usual longevity under such conditions ranged from 
3 to 6 days. Some adults captured in nature were kept under simi- 
lar conditions and lived from 3 to 5 days. 

Various flowers were supplied as food for the adults, but in no 
case was feeding observed. Sweepings were also made from flowers 
blooming in pastures and from alfalfa in bloom, but adults were 
never captured under such conditions. 

ADULT HABITS. 

Adult flies in cages copulate most frequently about noon, the 
(duration of the act ranging from 3 and 4 to 15 minutes. During the 
act the flies usually remain quiet, except, for the distinct abdominal 
movements of the male. The male usually breaks from the female, 
leaving her at the place of copulation, but within a few minutes may 
be observed to return. One pair has been observed to copulate as 
many as four times within an hour. Males will mate with a freshly 
emerged female before her wings are dry, properly unfolded, or the 
body of a normal color. In nature the one object of the male seems 
to be copulation, and that of the female oviposition. Buzzing in 
midair about the horse the male may be easily caught with the hand. 
A female is only observed buzzing at a standstill in midair when 



GASTROPHILUS HAEMOERHOIDALIS AND OTHER BOTS. 27 

a horse is gniEiiig or otherwise protected from ovipositions. She 
usually comes from a distance and strikes at the lips. Her quick 
flight seems to be distinguished by the male, who attempts to mount 
her before she oviposits, but the momentum of the two usually carries 
the couple to some distant place so quickly that one can not tell 
whether copulation actually takes place upon the wing or whether 
they fall to the ground. At any rate, they fly for some distance. Ap- 
parently the sexes always meet at the horse, the males awaiting the 
approach of the females. At times the male encounters an adult 
female of G. intestinalis about the horse, and these two may be ob- 
served to fall upon the grass at the feet of the horse, usually separat- 
ing within a few seconds. 

TREOVIPOSITIOX PERIOD AND OVIPOSITIONS. 

Just how soon after emergence copulation takes place is not 
definitely known, but it is certainly less than 18 hours. Adults 
emerging during the night copulate by noon of the following day 
and will oviposit during that afternoon. They will not oviposit in 
captivity. On five occasions in which flies emerged normally during 
the night, males and females were kept in a box with glass sides and 
with green foliage. By noon in each case some w^ere observed to 
copulate and when liberated in the afternoon would oviposit. Their 
wings were colored with red ink, and when captured they could be 
identified easily. Under favorable conditions ovipositions took place 
as soon as adults were liberated, usually about 3 hours after copula- 
tion. After a lapse of a few minutes they were never to be col- 
lected about the same bunch of horses, which is probably due to the 
migration of adults and to the movements of the various horses upon 
which they oviposit. 

A determination of the egg-laying period is important in that it 
shows the value of destroying adults at different times during this 
stage, but with such short preoviposition and longevity periods and 
the inability of flies to feed, the indication is that the flies oviposit 
throughout their existence. Dissections of females reared to adults 
indicate that they develop from 134 to 167 eggs, the usual number 
possibly being near 150. 

Unlike G. intestinalis, which may stand in midair and consecu- 
tively deposit 15 or 20 eggs at one time, often placing two or more 
upon one hair, G. haemorrhoidalis deposits but one at a time and 
only one upon a hair. 4t leaves the animal for about one-half minute 
or longer after ovipositing, but not for so long a time as does 
G. nasalis. It never oviposits upon any other portion except the 
lips, preferably the portions moistened by saliva. The stalk portion 
of the egg is inserted in the pore of the skin at varying depths, but 



28 BULLETIlSr 5!)7, U. S. DEPARTMENT OF AGRICULTURE. 

the stalk has never been observed to be inserted for its full length. 
Often it extends to such a slight depth that after a few daj^s the egg 
may be found lying lengthwise upon the lips, yet firmly attached to 
the hair. The color, a jet black, so conceals the attachment to the 
transparent hair that it appears that the hair extends through the 
center of the stalk portion and through a portion of the side of the 
egg. The extreme point, however, shows a folding about the hair 
which may be attributed to the pressure Avhen it is inserted in the 
pore of the skin. Above the stalk portion the hair is attached to 
the side of the chamber containing the larva in a similar manner to 
the attachment of other Gastrophilus eggs upon the hair. 

INCUBATION AND INGKESS OF LARV.^. 

Having observed eggs upon both moist and dry portions of the 
lips of horses, large numbers in various stages of incubation were 
removed and placed in tubes for observation. About 100 were kept 
in a test tube, with a moist cotton stopper, at the air temperature 
of a living room. While a variation in color was at first observed, 
ranging from a black to a reddish color, after a few days the major- 
ity were of a reddish brown. Some were placed upon a slide and 
moistened, then b}^ the use of two dissecting needles dead larvse were 
removed. Xo larva? had hatched of their own accord, but emerged 
when subjected to moisture and friction. In similar tubes which 
Avere kept dry three lots of eggs varying in color were observed and 
not a single larva hatched. 

Examinations of the inside of horses' lips revealed numerous holes 
accompanied by much soreness which appeared as though the young 
larvae hatched and had burrowed through the lips. Upon dissec- 
tions in post-mortem examinations it was disclosed thiit the injury 
Avas caused by " wild Ijarley " or " foxtail grass." This grass was 
determined by the Bureau of Plant Industry as Hordeuni ivhafum-. 
Its injuries are more noticeable upon lips of livery horses when feci 
hay containing this grass, as pastured animals avoid eating it and 
the injury is less noticeable. It is worthy of note that this grass, 
in addition to its injury upon lips of horses, serves as a winter host 
of the black rust which is so destructive to wheat in the Dakotas. 

On August 24, 1915, a suckling colt, its mother (a crippled horse) 
and another horse were carefully freed of eggs. Twent3^-four hours 
later a diagram was made showing the exact location of each egg 
deposited during this time. Upon the following three days it was 
too cloudy for other adults to oviposit, so the horses were not kept 
in a barn to prevent further ovipositions, but Avere left to graze in 
the pasture. This alloAved ample time for development of the 
embryo and of a distinguishing brownish-red color which greatly 
aided in keeping tratk of the eggs. 



GASTKOPHILUS HAEMOKEHOIDALIS AND OTHER BOTS, 29 

Upon the suckling colt the first egg disappeared upon the ninth 
day ; the eleventh day, two ; the thirteenth, five ; and the fourteenth, 
six. Five other eggs about 1 inch from the mucous membrane and 
upon the dry portions yielded dead larvse when examined. 

Upon the lips of the cripple horse and within 1 inch of the mucous 
membrane 15 eggs were deposited. The first 6 eggs disappeared 
upon the seventh day from near the corners of the mouth. The last 
egg disappeared upon the eighteenth day. 

The normal horse in grazing received 14 eggs within 1 inch from 
the mucous membrane. Upon the sixth day 10 eggs disappeared 
from near the corners of the mouth, which was probably five days 
from deposition. The other 4 disappeared during the following 
three days. 

The striking feature of the above three cases is that those eggs 
deposited where they received most moisture and friction were the 
first to disappear. Prior to disappearance, the color changes, being 
first brownish, then a brownish red, finally with a whitish tip, thus 
clearly indicating embryonic development. It is also clearly seen 
that the amount of grazing afi'ects the incubation, as the normal 
horse grazed practically the whole time, the cripple only at times, 
while the suckling colt was not observed to graze. There were no 
indications that the larvae burrowed into the lips, and as well-incu- 
bated eggs have produced larvae under moisture and friction when 
removed, it is certain that the method of ingress of larvae into the 
host is not unlike that of G. intestinaUs. It is true that eggshells 
were never found attached to the hairs after the larvae had emerged. 
but it is believed the moisture and friction are sufficient to remove 
these after the larvae leave the eggs and enter with the food. 

Incubation records are not confined to the above three cases. 
Upon August 24, 1915, one other animal was freed of eggs and 
allowed to receive depositions during 24 hours. Upon the moist 
portions of the lips 17 eggs were found, while 6 were deposited 
upon the dry portions 1 inch from the mucous membranes. Separate 
notes give a comparative idea of the incubation. Upon the sixth 
day, probably 5 days from deposition, 4 eggs disappeared from the 
moist portions and others disappeared the following day. Upon 
the dry portions all were present upon the twelfth day. Three of 
these when removed contained dead forms and the other 3 disap- 
peared from the eighteenth to the twenty-third day. 

The day of oviposition in the above cases was favorably followed 
by three cloudy days, which prevented other ovipositions. The de- 
velopment of the embryo in eggs upon moist portions was quite in 
contrast to those upon the dry portions, showing clearly the necessity 
of moisture and friction. Such observations indicated that those 



30 BULLETIN 597, U. S. DEPARTMENT OF AGEICULTUEE. 

eggs upon the moist i^ortions incubated in from 5 days to a slightly 
longer period. 

September 9 was preceded by two unfavorable days for oviposition 
and was itself very favorable, but was followed by rain and cloudy 
weather until September 15. At this time black eggs were found 
upon the dry portions of the lips, while upon the moist portions 
the eggs were reddish with whitish tips. Due to the scarcity of 
adults, the eggs were not plentiful at this time, and a few days 
later one only could be found, upon the dry portions of the lips. 

Due to the comparatively long period during which the eggs re- 
main attached upon the dry portions of the lips of horses, which is 
particularly due to the protection of the thick, coarse hairs surround- 
ing them, it is believed that one could be misled easily as to the 
most favorable places of deposition of the adults. 

GASTROPHILUS NASALIS (Linnaeus). 

SYNONYMY. 

Oestrus nasalis Linnaeus, 1761. 
Oestrus veterinus Clark, 1797. 
Oestrus salutiferus Clark. 1815; 
Oestrus clarkii Leach, 1817. 
Gastrus nasalis Meigen, 1824. 
Oestrus duodenalis Schwab, 1840. 
Oastrophilus nasalis Schiner, 1861. 

OVIPOSITIONS AND LONGEVITY. 

The female GastropMlus nasalis often appears from the grass 
about the fore legs of a grazing animal, strikes under the jaws, re- 
mains a few seconds, and during that time deposits an egg about 
midway upon the hair. The adult then leaves, completely disap- 
pearing in the distance, but within a minute or two a similar oviposi- 
tion may occur, except that the adult approaches from a distance. 
The presence of a person about the head of an animal does not inter- 
fere with egg deposition, and the fly may be caught with the hand 
when it alights upon the hairs underneath the jaws. It may also 
be observed to deposit upon the fore legs or the flanks. Dissections 
of the abdomen of reared females show that they are capable of 
depositing from 480 to 518 eggs. The attachment of these, as may 
be seen by referring to figure 3, c, extends to almost the entire length 
of the egg, and being attached about midway upon the hair, numbers 
are concealed unless the hair is brushed aside in making examina- 
tions. Often eggs may be observed near the end of the hairs, but 
this usually occurs after great numbers have been deposited. Then 
it is possible to find two or more eggs upon one hair. As yet the 
method of ingress of the larvae has not been determined. Dr. C. H. 
T. Townsend thinks that the larvae burrow through into the mouth 



GASTEOPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 



31 



and are swallowed. One anthor believes that a horse in eating will 
rub the jaws upon the manger, which hatches the eggs, and that they 
are taken into the mouth with the food. The fact that some eggs are 
deposited upon the fore legs and portions accessible to the mouth 
indicates that the ingress of larvae may be similar to that of G. intes- 
thuilis. 

Longevity in this species seems to be increased over that of 
G. haemorrhoidalis^ as one reared adult kept under conditions similiir 
to those of the nose fly lived for 12 days. 

LARVA AND PUPA STAGES. 

Coincidentally with the appearance of G. haemorrhoidalis at the 
anus of horses, the larvse of G. nasalis occasionally may be observed 
to pass normally from horses and be found in their droppings. This 
normally occurs when larvse become fully developed and is often 
attributed by farmers to " a destructive effect of grass upon the bots." 

These larvse seldom migrate a great distance, and apparently only 
burrow under the droppings for protection. Larvae which dropped 
normally pupated in from 1^ to 2 days, though the prepupal periods 
in some cases in which larvae were removed in autopsies and cited in 
Table YII extended for 7 days. It was observed that the short pupal 
periods were preceded by long prepupal ones, and that larvEe pupat- 
ing within 2 days after dropping emerged in from 42 to 45 days. 
At Victoria, Tex., Mr. J. D. Mitchell collected a larva under manure, 
which pupated October 6, 1914, and emerged 20 days later. To 
rear larvae collected in autopsies is a difficult task, even though they 
are well developed and appear normal, but during the late summer 
a small percentage may be reared if they are collected from horses 
immediately after death. The larvae removed from dead animals 
are capable of remaining alive and active for some time, some having 
been kept as long as 25 days. Some larvae have been observed to 
live submerged in water for 12 days. 



Table VII. — Pupal periods of Gastrophilus nasaUs, Aberdeen, 


S. Da 


k., 


1915-16. 


Larvte 


Location. 


> 


Breeding environ- 
ment. 


i 

a 

3 
u 

S 

2; 


1 

ft 
3 

.— o 

or 

o 

§ 


Number 
emerged. 


8 . 


Temperatures. 


col- 
lected. 


9> 


_2 


k6 


5^ 


d 

a 


1915. 
June i 


Fresh dropping 

do 


1 

2 
4 

19 

18 
18 


With horse manure. 

Clean tin box; moist 

sand. 
do 


1 

2 

1 

3 
3 
3 


Days. 

42 

44-45 
31 

25-33 

48 
56 


1 
1 

1 

1 

1 
1 




Days. 


"F. 

88 

94 

94 

98 
98 
95 


"F. 
35 

42 

42 

41 
28 
28 


°F. 
65.30 


1916. 
May 29 

June 12 


1 

2 
...... 


7 

3-15 

3-8 

11 


67.93 


Dropped from treat- 
ment. 
Duodenum 


1 68. 98 


July 10 
Aug. 11 


Dry paper in tin box. 
Moist sand . . 


72 77 


Stomach 


60 26 


11 


Duodenum 


.. do 


59.97 











1 Horse treated with carbon disulphid. 



32 BULLETIN 591, U. S. DEPARTMENT OF AGRICULTUEE. 

GASTROPHILUS INTESTINALIS (DeGeer). 

SYNONYMY. 

Oestrus hovis Linnaeus, 1761. 
Oestrus intestitialis De Geer, 1776. 
Oestrus equi Clark, 1797. 
Oastrophilus equi Leach, 1817. 
Gastrus equi Meigen, 1824. 
Oestrus gastricus major Schwab, 1840. 

OVIPOSITIONS AND LONGEVITY. 

The universal distribution of the common bot-fly, the familiarity 
of innumerable persons with its oviposition habits, and the numerous 
publications dealing more particularly with ovipositions and ingreps 
of the larvse into the host since Bracy Clark (1797), leave little to be 
desired. It is probable that there is no other insect whose eggs come 
so directly under the observation of farmers as does the common bot- 
fly. The common names of this Gastrophilus vary with the locality, 
but farmers a'^e usuall}^ aware of the fact that this insect produces the 
bots in horses. 

Some authors contend that the eggs are deposited upon those 
places most accessible to the horse^s mouth, while others hold that 
the fly will deposit upon any portion where it is not disturbed. 
It has always been observed that these flies give preference to the 
forelegs, and, after these have become well covered with eggs, depo- 
sitions occur at other points where the fly is not disturbed by the 
horse's tail. Very few eggs are deposited upon the hind legs or upon 
the backs of the animals, but when adult flies are in numbers the 
mane may become heavily infested, especially near the shoulder. 
Large numbers of eggs may be found upon the sides of the animals, 
and these are concentrated at points accessible to the mouth, as in 
cases of depositions upon the inside of the forelegs. It seems that 
the fly oviposits on the forelegs instinctively, and, after the legs 
become heavily infested, adults may be observed to deposit one or 
two eggs on them and then seek other portions of the body. At times 
two or more eggs may be found upon a single hair on the inside of the 
forelegs, but seldom has this been noted upon other portions. How- 
ever, the length of the mane often permits adults to deposit large 
numbers upon a single hair. With the exception of the forelegs, the 
sides below and to the rear of the shoulder blades probably harbor 
most eggs. 

The longevity of 14 reared adults in 9 tests, in which the flies 
were kept under conditions similar to those employed in rearing G. 
Jimmorrhoidalis varied from 7 to 21 days. The longer periods oc- 
curred during early fall, when lower temperatures were experienced. 
These adults, like those of other species of Gastrophilus, were never 



GASTEOPHILUS HAEMOKKHOIDALIS AND OTHER BOTS. 33 

observed feeding upon flowers, but green twigs were favorable resting 
places in rearing cages. 

A female taken while ovipositing was placed within a tube contain- 
ing a male, and they were observed to copulate for 5 minutes. 

Dissections of 5 females showed the following egg capacity : Maxi- 
mum, 770; minimum, 397; average, 541, 

INCUBATION AND INGRESS OF LARV^. 

While making observations in pastures, on four occasions large 
numbers of eggs were collected which had been deposited upon the 
author's horse. The eggs were kept in tubes at air temperatures of a 
living room and none hatched without friction and moisture. By 
placing the infested hair upon a microscope slide and moistening it 
the larvse were most easily removed by rubbing the lot with a dis- 
secting needle. In such tests the eggs remained attached to the hair, 
while the operculum was removed, allowing the larva to emerge. 
Very good results were also obtained by rubbing a moistened finger 
over the lot. When eggs were less than 7 days old it was found diffi- 
cult to obtain living larvae, though at 9 and 11 days active larvae were 
removed. When they were slightly older than 11 days they emerged 
without difficulty when attended by moisture and friction, and one 
living larva was found as late as the forty-eighth day. This seemed 
to be an exception, as in the other lots all were dead after 40 days. 
In general, all experiments tended to confirm those of Osborn. Ac- 
cording to Guyot, with various lots placed in paper bags and kept 
in a pasteboard box at room temperatures, some emerged without 
moisture and friction. On December 28, 1900, Guyot obtained 
quite agile larvae as late as 96 daj^s after collection of the eggs. 
In another case, with eggs collected on October 6, he succeeded 
in obtaining larvae from January 7 to 13 following, a period of 92 
to 98 days. Due to this fact, Guyot concludes that the larvae are 
capable of withstanding comparatively low temperatures after the 
eggs have been removed from the host. From eggs collected on 
horses in the open, active larvae were removed as late as December 1. 

LARVA STAGES. 

The attachment of young larvae frequently occurs in almost any 
part of the stomach, but, as has been previously stated, they are 
found as fourth-stage larvae upon the mucosa of the stomach, more 
especially on the left sac. If living larvae are removed from an 
animal during a post-mortem examination a great tendency for re- 
attachment will be observed. During such examinations they have 
been frequently separated into lots according to species, and in a short 



34 BULLETIN 597, U. S. DEPAETMENT OF AGRICULTUEE. 

time they would attach to a piece of paper or stomach section or even 
to one another. This is only a temporary attachment, however, and 
apparently no attempt at feeding takes place. 

The studies of Braner, Numan, and Giiyot indicate that the larvae 
molt during their development and that there are at least three 
stages. No experiments have been reported as to the exact time that 
larvae remain within the body of the horse, although apparently they 
spend about 10 months in this parasitic stage. On some occasions, 
as will be observed in Table I, well-developed larvae were disclosed on 
post-mortem examinations in early fall. The indications are that 
some larvae are not sufficiently developed to pass out in time to pro- 
duce adults and that they succumb to low temperatures. There are 
various factors that apparently tend to influence the extension of lar- 
val periods. When gross infestations occur the development is 
markedly slower than in those horses containing only a few" larvae. 
I^axative foods have a greater tendency to discharge well-developed 
larvae than foods of a non-laxative nature, as is observed in comparing 
autopsies of livery and pastured animals. Since there is such a wide 
range of variation in the ages of larvae within the eggs at which they 
are capable of being ingested it is possible that this may tend to 
prolong the period during which the last-stage larvae drop. 

SUBMERGENCE OF hARVJE. 

Last-stage larvae removed from horses immediately after death 
remained alive and active from 21 to 33 days when submerged in 
water, but when submerged for only 6 daj^s they would not attempt 
pupation. These periods are considerably decreased if larvae are 
not removed shortly after the death of the animal. 

PUPA PERIODS. 

The larvae drop naturally with manure, burrow only enough for 
protection, and normally pupate within a day or two. The periods 
of dropping extend over a long time and very few larvae are 
found in droppings. It is a difficult matter to rear larvae taken 
in post-mortem examinations, and this is best undertaken in the late 
summer or early autumn, when the greatest number of larvae are 
fully developed. With such larvae, used in the experiments, the pu- 
pa periods have been observed to vary from 27 to 43 days, with an 
average of 38 days. 

EFFECT OF DEATH OF HOST UPON GASTROPHILUS LARV^. 

The resistance of larvae and the death of horses from infectious 
diseases naturally suggest the fate of larvae during the period when 
they normally drop. In experiments larvae were not kept with the 
animals during the decay, but were removed in autopsies, separated 



GASTEOPHILUS HAEMOEKHOIDALIS AND OTHER BOTS. 35 

according to species, and placed under favorable rearing conditions. 
It is evident that larvae within the stomach and duodenum are not 
capable of withstanding the internal processes which accompany 
the decomposition of animal tissues, especially during warm periods. 
There is excessive gas formation with the breaking down of the tis- 
sues, and the larvre apparently become asphyxiated, since they are 
found bloated and when crushed become flat. During cool periods 
larvsB are affected very little for a number of hours, and in stated 
cases as long as 30 and 48 hours after death of the host larvae have 
been reared to adults. Low temperatures hold back that period of 
decay in the carcass which normally would cause the death of larvae. 
From post-mortem examinations, as will be seen in Table I, 
G. haeTnon^hoidalis larvae are seldom found in the rectum. In all 
probability they drop shortly after death, and during the normal 
period of dropping are capable of producing adults. 

CONTROL STUDIES. 

REMOVAL OF G. HAEMORRHOIDALIS LARV^ FROM RECTUM. 

The effectiveness of the extraction of Hypoderma larvae as advocated 
by various authors suggests a mechanical removal of G. haemorr- 
hoidalis larvae. While they appear at the margin of the anus daily, 
studies show that they remain visibly attached from 40 to 71 hours. 
This would necessitate much work during a busy season with farm- 
ers, but extractions at feeding time would greatly reduce the number 
in work animals. In practice this periodical detaching caused much 
discomfort and soreness about the anus. 

The attachment of clusters of larvae within the rectum and the 
recommendation of tobacco decoctions, by the Bureau of Animal 
Industry (1911), for larvae lodged in the rectums of horses, indi- 
cated the need of information as to the effect, on this species of 
Gastrophilus, of substances used as enemas. This necessarily re- 
quired a detailed study of the effects of various substances upon 
larvae, and these are reported in Table VIII. 



36 



BULLETIN 597, U. S. DEPAETMENT OF AGRICULTUEE. 



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38 BULLETIN 597, U. S. DEPAETMENT OF AGRICULTUEE. 

Some of the tasnicides and larvicides which have been successfully 
used upon insects, as well as soapy enemas, were tested upon detached 
larvae in tin boxes. As with other Gastrophilus larvae, remarkable 
resistance was noted. It will be observed that negative results were 
obtained by using the common tsenicides, that soap solutions seemed 
more effective, and that nicotine sulphate gave good results. 

LARVAL TREATMENTS. 

Experimenters have been impressed with the resistance of Gastro- 
philus larvae to various contact substances, and it is practically 
agreed that any contact substance capable of killing the larva would 
seriously injure the stomach membranes of the horse. The internal 
method for use must necessarily be in the form of a fumigant. The 
use of carbon disulphid internally, as brought out by Perroncito and 
Bosso, has been tried and indorsed by many veterinarians. A list of 
indorsements from many countries can be found in articles dealing 
with this subject. Originally the disulphid was administered in 
12-gram capsules surrounded by aloes, the whole contained in 48- 
gram gelatine capsules. In the hands of various workers it has been 
subjected to modifications, but each reports that large numbers of 
larvae pass as a result of the treatment, and some remark upon the 
beneficial effects of the removal of larvae upon the animal. 

The Bureau of Animal Industry, after employing this treatment 
upon a number of horses, recommends the following procedure : 

The day preceding the treatment a small amount of hay and a moderate 
amount of oats is given in the morning ; in the evening food is withheld and a 
purgative given — Barbados aloes 1 ounce, or raw linseed oil 1 pint. The day of 
the treatment, at 6 o'clock in the morning, give 3 drams of carbon disulphid in 
a gelatin capsule; at 7 o'clock repeat the dose in the same manner-, and at 
8 o'clock give the third and last dose, making in all 9 drams of carbon disulphid 
in three gelatin capsules. 

The above treatment is for the adult horse. For a yearling colt half the 
quantity of carbon disulphid used for a mature horse will give the desired 
results. If properly administered the gelatin capsule reaches the stomach 
intact, but soon dissolves and the carbon disulphid rapidly evaporates, suffo- 
cating all hot larvae and other parasites with which it comes in contact, but 
not injuring the horse. Worms are quite often expelled as well. 

The Bureau of Animal Industry calls attention to the fact that 
the so-called 4-dram capsules hold about 3 drams of carbon disulphid. 

Desiring to know the periods of time required to kill the larvae in 
the treatments, a number of experiments have been conducted in 
fumigating stomach sections to which larvae were attached. Only 
larvae from those animals that could be secured shortly after the death 
of the hosts were used, and the sections with larvae in situ were placed 
in wooden boxes tightly covered with glass after the box was well 



GASTROPHILUS HAEMOERHOIDALIS AND OTHER BOTS. 39 

moistened. The sections came from both the stomach and duodenum, 
and the tests inchide all three species of Gastrophilus. After the 
short periods of fumigation, which were ineffective with last-stage 
larvae, it was observed that the larvae lived for some days. At the end 
of fumigation tests it was impossible to determine the viability of 
larvae except by observing them for a number of days. As will be 
seen in Table IX, chloroform was not wholly effective at 4 hours, 
but at a later date larvae were killed with carbon disulphid within 
3 hours. In no case did larvae live after subjection to 3^ hours of 
carbon disulphid. These gases were liberated from absorbent cotton 
in the corner of the box, and no larvae came in direct contact with the 
liquid, as would probably be the case within the stomach. The carbon 
disulphid, being soluble in water, evidently reaches all portions of 
the stomach, either as a gas or in solution. 



40 



BULLETIN 597, U. S. DEPAETMENT OF AGRICULTURE. 









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42 BULLETIN 597, U, S. DEPARTMENT OF AGRICULTURE. 

The G. intestinalis are the most resistant of the Gastrophilus to 
treatments, but these, being found in the stomach, are in the most fa- 
vorable place for treatment. No immediate effects of the gas upon last- 
stage Gastrophilus larvae are observed, as they remain motionless for 
some time. Finally they contract so as to conceal the hooks of attach- 
ment and then drop from the stomach section. This sometimes occurs 
within 30 minutes after the fumigation begins, but most often it is 
after 1 or 2 hours. Occasionally the contraction is not so great and 
larvae remain attached but drop at the slightest touch. A number of 
observations were made upon animals treated by local veterinarians. 
During the spring and early summer records were kept on 23 of these 
horses, which were treated when they contained only last-stage larvae. 
The treatment was given as recommended by the Bureau of Animal 
Industry. Within 36 to 48 hours the first bots appear in the faeces, 
though if the physic acts well they may be found after 24 hours. The 
writer observed bots to pass for a period of 5 days, beginning about 
36 hours after the treatment. With the first droppings a few living 
larvae may be found which detached from the stomach before the 
treatment, and in one case G. nasalis was reared from such larvae. 
G. haemorrhoidalis may appear at the anus as usual if this treat- 
ment is given in the spring, as by this time numbers have previously 
migrated to the rectum. 

While Table IX shows that carbon disulphid gas is callable of 
killing last-stage larvse within 3^ hours, the ideal time for treatment 
of horses would be in the autumn when all larvae are young and the 
G. haemon^hoidalis are still within the stomach and duodenum. The 
last-mentioned experiments in Table IX show some fumigation re- 
sults with small Gastrophilus. It will be observed that 1 hour was 
an amply sufficient time, though a few last-stage larvae were present 
as late as September 18. If not caused to detach these would possibly 
drop during the winter and succumb to low temperatures. In Dallas, 
Tex., 45 minutes was sufficient to kill young larvae on December 9, 
1916. 

The fact that G. nasalis attaches in the throat, where the larvae are 
Dot in a position to be affected by the carbon disulphid treatment, em- 
phasizes the fact that " an ounce of prevention is worth a pound of 
cure." 

REPELLENTS. 

The rubbing of horses upon posts, bowlders, and other convenient 
objects suggested a device for use in pasture whereby horses could 
rub their lips upon a repellent. The short period of effectiveness of 
repellent substances and the inability to obtain one that will remain 
on the lips during grazing are difficulties which would seem to be 
overcome by such a device. A keg reservoir was devised whereby a 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS, 43 

flow of repellent, which was regulated by a stopcock, moistened a 
padded plank by means of a small pipe perforated with holes. This 
was placed at a salting and resting place of the horses and the amount 
of rubbing noted was very encouraging. Unfortunately, the horses 
did not rub the corners of the mouth, which are favorable places of 
egg deposition, and the scheme was abandoned. 

Dr. Van Es suggested the use of a repellent upon the forelegs of 
horses and other portions of the body accessible to the mouth, so 
lis to cause the common bot fly to deposit eggs upon places where they 
could not be reached by the horse's mouth. A marked repellent 
quality was observed in equal parts of pine tar and lard, no adults 
having been observed to oviposit during the following 4 days. There 
was apparently no injury to the animal, and 1 part of tar to 2 parts of 
lard was effective during 3 days. The disadvantage in some of the treat- 
ments was the fact that animals would walk through mud and water 
and cause a decrease in the repellent qualities of the mixture applied. 
Very good results were obtained with pine tar 3| ounces, kerosene 
1^ ounces, laundry soap 1 ounce, powdered resin 1 ounce, and hot wa- 
ter to make 14 ounces. The pine tar was thinned with kerosene, the 
soap and resin dissolved in hot water, and the two mixtures poured 
together. There was not only great repellent action observed, but 
the resin caused the hair to stick together in small bunches and pre- 
vented the adult flies from ovipositing. There was apparently no 
injury to the skin of the animal, and these same repellents pre- 
vented G. nasalis from ovipositing under the jaws. A successful repel- 
lent that would not require renewal over a reasonable period is de- 
sirable, since the loss of time due to the renewal of repellents is a 
great loss. 

MECHANICAL PROTECTIVE DEVICES FOR WORK HORSES. 

The protective devices found upon work animals vary, but there 
are none used in the Dakotas on pastured animals. (See Plate V.) 
Various forms of fringes are most frequently found and may consist 
of leather, burlap, or a portion of the leg of trousers. These are 
probably the least effective of the devices, as examination of teams 
wearing such fringes developed the fact that they are often found 
infested with eggs. Leather seems to be the most efficient of the 
fringes, as it is not so easily blown aside by the wind and does not 
hinder the horses in breathing. Those extending completely around 
the head retail for 50 cents each, while those covering only the face 
sell for 25 cents. 

Baskets which are used extensively in nose-fly districts serve as 
muzzles during the last plowing of corn, but are not very effective 
nose-fly protectors. The mesh is of sufficient coarseness to permit 
flies to oviposit if the lips can be touched. They do not always fit 
well at the top and occasionally a nose fly will get on the inside, 



44 BULLETIN 597, U. S. DEPARTMENT OP AGEICULTTJRE. 

producing great annoyance by its buzzing. During thrashing 
moisture collects within the basket and, when the dust settles upon 
this, creates a condition which greatly handicaps the animal's breath- 
ing. These baskets retail for 35 cents each when fitted with two 
snaps. 

While protection of any description about the lips will prevent 
many ovipositions and annoyance by flies, by far the most effective de- 
vice consists of a simple strip of leather extending over the lips and 
fastened at the bit rings. This actually covers the portions of 
the lips upon which the flies lay their eggs and upon horses thus pro- 
tected an absence of eggs and annoyance has been noted. During the 
movement of the horse's head in walking, especially when working, 
this protection not only covers the lips, but swings to and fro and 
tends to repel the flies. The nostrils being exposed, it does not hinder 
breathing. Due to the cost of leather, very few of these are in use, 
but if one obtains an old belt from a thrashing machine great num- 
bers can be made. It requires only a strip which will extend from 
one bit ring to the other and be from 4 to 6 inches in width. The size 
of the strip will depend upon the size of the horse's head. A snap 
placed at each end near the center facilitates handling, and the pro- 
tector can be snapped onto the harness when not in use. 

PROTECTORS FOR PASTURED ANIMALS. 

Studies of efficiency of halter appliances for pastured horses have 
been made, and while conclusive results have not been obtained, a 
type has been designed which promises to meet the demand. At 
first halters were used Avith a piece of leather covering the jaws and 
hanging so as to flap against the lips when the animal walked. The 
front of the halter was provided with a face net which swung over 
the nostrils and lips. This proved unsatisfactory, as the flap, if 
long enough to protect the animals during depositions, was too long 
during grazing. The horses would step upon them with the fore 
feet, causing them to break. 

A variation from the most efficient work-horse protector was 
devised by using a piece of duck on the rear, so as to cover the jaws 
and prevent G. nasalis from depositing in this location (see fig. 4). 
A block of wood under the center and below the lips enables a horse 
to graze with ease and at the same time be protected from flies when 
the head is held above the ground. The cloth on the rear also pre- 
vents ingress of G. intestinalls larvae by preventing the horse from 
scratching portions infested with eggs. When the head is placed 
upon other animals the device occasions such discomfort that almost 
immediately the horses move and prevent the protected animal from 
becoming infested from their bodies. 

For pasture uses the leather becomes soft and at times exposes the 
corners of the mouth, but excellent results have been obtained by sub- 



Bui. 597, U. S. Dept. of Agriculture. 



Plate V. 




Devices in Use to Protect Work Horses from Ovipositing G. Haemorrhoidalis. 

Upper left.— A leather f rings is fairly effective. Upper right.— A burlap fringe hinders breathing. 
Lower left.— A wire basket often permits ovipositions on account of coarse mesh and ill fitting. 
Moisture and dust collect and hinder breathing. Lower right.— A strip of leather actually 
covers oviposition places and allows the horse to breathe easily. (Original.) 



I 



GASTKOPHILUS HAEMOKRHOIDALIS AND OTHER BOTS. 



45 



stituting a hard wood. The weight in either case will compare with 
the weight of blind bridles. Horses using these in experiments be- 
came free of G. haemorrhoiddlis eggs during the summer of 1916, 
whereas unprotected animals were heavily infested. There was also 
a marked difference in the feeding, as protected animals grazed nor- 
mally in bunches. 
While the device in- 
dicates a favorable 
preventive measure, 
before its adoption 
tests of durability 
should be made and 
minor points in the 
construction deter- 
mined. It seems pos- 
sible that the con- 
struction could be 
made so simple that 
farmers could make 
the protectors at a 
nominal price. 

A halter attach- 
ment would permit 
horses to graze dur- 
ing times that are 
favorable for depo- 
sitions of flies, and 
would prevent even- 
tual infestations by 
all three species of 
Gastrophilus. A 
shed constructed in 
the pasture would 
protect animals 
from nose flies, al- 
though it would not 
prevent infestations 
by the other species 
of Gastrophilus. 
Such a shed would keep the animals from grazing during times that 
were favorable for depositions, and could be used for storage of feed 
during the winter. 

EFFECTIVENESS OF WASHES UPON EGGS. 

Regardless of whether horses are treated internally for bots, which 
is best during the autumn, when larvse are small, or Avhether they 




Fig. 4.- — A bot preventive. The box prevents " nose flies " 
from ovipositing when the head is held upright, while the 
block of wood underneath the box allows the horse to 
graze easily. The canvas prevents normal ovipositions of 
the " throat bot-fly," and does not permit the horse to 
bite the portions infested with eggs of the " common bot- 
fly." (Original.) 



46 



BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 



wear halter appliances during the summer, it is necessary to treat 
the eggs during the autumn to prevent a late infestation from the 
well-incubated eggs after the protectors have been removed. Then, 
too, the ease with which places so accessible to the horse's mouth can 
be washed makes the use of w^ashes a practical prevention in regions 
where bots are not so numerous. 

L,A1XVM REMOVED FROM EGGS PRIOR TO TREATMENT. 

Active larvae were removed from well-incubated eggs and subjected 
to substances reported in Table X. Only larvae in excellent condition 
were used, and these were observed in watch glasses, small tin boxes, 
and test tubes at short intervals until dead. When in doubt they 
were removed with a drop of the liquid to a microscope slide, and the 
warmth of one's breath was sufficient to cause living ones to move. 
Larvie were killed instantly when placed in volatile liquids or gases 
of carbon disulphid and in absolute alcohol. 

Table X. — Resistance of first-starje larvw of Oastrophilus intestimilis, Aberdeen, 

S. Dak., 1916. 



Larvae placed iu— 


Longevity. 


Larvae placed in— 


Longevity. 




72 to 126 hours. 
76 to 99 hours. 
24 to 36 hours. 
20 to 28 hours. 
41 to 48 hours. 
28 to 41 hours; 
24 to 43 hours. 


Borax, saturated solution 

50 per cent alcohol 


40 minutes. 




30 minutes. 




Petroleum, refined 


30 minutes. 


Bcta-naphthol in alcohol... 

10 per cent oil of tar emulsion 

Borax, saturated solution 

Do 


Do 


30 minutes. 




13 minutes. 


33§ per cent pine tar and 66i per 
cent kerosene. 


1 minute. 







Dr. Guyot's results compare favorably with those herein reported. 
His larvae remained alive in water for 4 days, nearly a day in olive 
oil, and more than 14 hours in bichlorid of mercury solution 1 to 
1,000. 

The movement of freshly emerged larvae is very rapid upon moist 
surfaces, but upon a dry surface they seldom move from tlie original 
location, although they have been observed to live for 72 to 125 
hours. When placed in water the larvae became submerged with the 
exception of the posterior spiracles, which remained exposed at the 
surface. They are capable of living in this manner for 76 to 99 
hours. 

LARV^ REMOVED AFTER TREATMENT OF EGGS. 

Hundreds of eggs were collected from horses in pastures during 
the latter part of August and the early half of September. At this 
time the activities of adults of G. infestinalis were being directed to 
the manes of horses for oviposition, as in most cases the inside of the 
forelegs and sides immediately behind the forelegs were very grossly 
infested. These hairs were of sufficient length to render handling 
easy, and the eggs were about the same age. Except as otherwise in- 



GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 



47 



dicated in Table XI, infested hair was placed in tubes at air tempera- 
tures of a living room and allowed to remain until larvse were well 
formed and ready for emergence. Some of the eggs were then tested 
and the viability determined. A check was not kept, as the brownish 
color of the dead larvae easily distinguished them from the trans- 
parency of the active larvae. 



Table XI.- 



-Effcctiveness of icashes upon eggs of Gastropfiiluft intestinalis, 
Aberdeen, S. Dak., 1915-16. 



Date 

eggs 

treated. 



1915. 
Sept. 
Do. 



1916. 
Sept. 7 
Do...- 
Do.... 

Do.... 

Do.... 

Do.... 

Sept. 9 

Do.... 

Do.... 

Sept. 11 
Do.... 
Do.... 
Do.... 
Do.... 
Do.... 

Do.... 

Sept 15' 

Do.i.. 

Do.i.. 
Do.i.. 
Do.'.. 

Do.-'.. 



Insecticide. 



Refined petroleum. 
do 



Kerosene 

1.35 per cent phenols ' — 

2 per cent nicotine sul- 
phate. 

Carbolic acid 2 per cent 
phenol. 

Lard 

Nitrobenzine gas 

Carbolic acid 2 per cent 
phenol. 

Kerosene 



0.135 per cent phenols 



Nitrobenzine gas 

do 

...do 

0.054 per cent phenols i . . . 

Kerosene 

2 per cent nicotine sul- 
phate. 

2 per cent carbolic acid. . . 

Kerosene 

Carbolic acid 2 per cent 
phenol. 

0.054 per cent phenols i . . , 

Kerosene 

Carbolic acid 2 per cent 
phenol. 

0.054 per cent phenols i . . . 



Ex- 
posure. 



Num- 
ber 

larvse 
ex- 
amined. 



Minutes 
6-lS 
18-31 

Hours. 
24 
24 
24 

24 

24 
25 
5 

29 

29 

4 

10 
25 
26 
25 
26 

26 
24 
24 

25 
147 
146 

147 



Mortality of larvae. 



Dead. 



Living. 



Doubt- 
ful. 



Remarks. 



Engine oil. No. 1. 
Do. 



Reddish brown in color. 



2 larvDs yellow in color. 

5 dead larvae yellow in 
color. 

3 dead larvae yellow in 
color. 



18 larvae very active. 
38 larvae very active. 



1 A proprietary compound of cresol in combination with resin soap. 

2 Eggs not well incubated were treated and larvae removed Sept. 21. 

In the tests with larvae removed from the eggs it was observed 
that the minimum period causing death by contact was 1 minute 
with pine tar 1 part and kerosene 2 parts. The ease with which 
either of these can be obtained suggested a study of these and similar 
substances. 

It will be observed that kerosene, which is commonly reported 
to be in use by farmers, even at an exposure of 147 hours, had prac- 
tically no effect upon larvae. When eggs upon hair were rubbed 
they more readily yielded to hatching and apparently the larvae were 
more active than from any similar treatment. The kerosene seemed 
to facilitate the emergence of the larvae. While it was ineffective 
against well-developed larvae, it was thought that upon freshly 



48 BULLETIN 597, U. S. DEPARTMENT OF AGEICULTUEE. 

deposited eggs it would probably prevent development of the embryo, 
as is the case with hens' eggs during incubation; but even a test of 
this kind was only slightly effective. 

A 2 per cent nicotine-sulphate solution was only partially effective. 
Nitrobenzine gas, wdiich has recently been brought to our attention 
as a fumigant for external parasites of animals by Prof. William 
Moore, of the University of Minnesota, yielded good results at 25, 
24, and 10 hours' exposure, but onh^ a small percentage was killed 
at 4 hours. The fumigation was conducted in a common glass fruit 
jar into which a strip of cloth, impregnated with a few drops of 
nitrobenzine, was suspended. 

The phenol compounds, by a contact application, seem to be most 
effective in destroying young larvae and preventing the further de- 
velopment of embryos. It will be observed that carbolic acid con- 
taining 2 per cent phenol yielded as good results as higher per- 
centages, and that this substance was most effectively used. 

With carbolic acid as a wash it will be well to be cautious of its 
effects upon the hands. If used at too great strength, the exposed 
skin of the hand will become white and peel off, although it does 
not affect the skin of the horse, which is protected by the hair. 

SUMMARY. 

Three species of horse bots — the common bot-fly {GastTophUus 
intestmalis) , the throat bot-fly {G. nasalis), and the nose fly {G. hae- 
morrhoidalis) — occur in the United States, and each is a source of 
considerable injury to horses. This injury is produced through 
worriment caused by the flies at the time the eggs are laid and by the 
attachment of the larvae, or bots, in the alimentary tract. 

Gastro'philus intestinalis and G. nasalis are widely distributed in 
the United States but G. haemorrhoidalis is confined to the North- 
Central and northern Rocky Mountain States. 

The nose fly {G. haemorrhoidalis) is by far the most annoying to 
horses at the time its eggs are laid. The adults appear early in June 
and reach the maximum of abundance during the first half of the 
season, disappearing with killing frosts. The eggs are deposited on the 
minute hairs on the iips, and those near the edges which are kept moist 
and receive friction hatch in from 5 to 10 days. The larvae are taken 
in with food or water and attach themselves to the walls of the 
stomach. Here they remain until the following winter or spring 
and then migrate to the rectum, where they reattach. Before leaving 
the host they usually attach close to the anus and protrude from it. 
They remain in this position from 40 to Tl hours. After dropping 
to the ground the bots seek protection and pupate in from 18 to 170 
hours later. The pupa stage lasts from 21 to 68 days. The adults are 



GASTBOPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 49 

very active, and as they deposit only one egg at a time thej^ are not 
so frequently seen about horses as are the adults of the common bot- 
fly. They take no food in the adult stage. Their length of life is 
from 1 to 7 days. 

The throat bot-fly {G. nasalis) deposits its eggs on the hairs under 
the jaws and to some extent on the shoulders and other parts of the 
host. The larvae of this species attach themselves to the walls of the 
pharynx and also to those of the stomach and duodenum. They do 
not reattach in the rectum or at the anus as do the bots of the nose 
fly. Pupation occurs in from 1^ to 2 days after the larvse have 
passed from the host, and adults emerge in from 20 to 56 days later. 
The adults are somewhat longer lived than those of the nose fly. 
The flies cause considerable annoyance to horses during oviposition 
but not as serious as in the case of the nose fly. 

The common bot-fly {G. intestinalis) usually appears later in the 
season than the nose fly and becomes most abundant just before kill- 
ing frosts. The eggs are deposited on all parts of the body, but 
preferably on the fore legs. They hatch upon the application of 
moisture and friction. From 9 to 11 days after oviposition appears 
to be the most favorable period for hatching, although some may 
hatch as early as 7 days and others as late as 96 days after oviposi- 
tion. The larvae attach in any part of the stomach, but the last-stage 
bots are found mostly in the left sac. They continue to drop from 
the host for a long period of time. Pupation takes place in protected 
places on the surface of the soil and the pupa stage lasts from 40 to 
60 days. 

All Gastrophilus larvae are surprisingly resistant to chemicals. 
The treatment of horses with carbon disulphid in three doses followed 
by a physic is satisfactory if administered in the late fall. Spring 
treatment is less effective, as the full-grown larvae are more resistant, 
and many of the nose-fly bots have left the stomach and passed back 
to the rectum at that time. 

Larvae of G. haemorrhoidalis may be removed from the rectum 
mechanically, but this is laborious. The use of enemas containing 
insecticides is ineflFective. 

As a repellent, pine tar mixed with other material gave good re- 
sults against the common bot-fly and the throat bot-fly. Such mix- 
tures may be utilized to cause the flies to lay eggs on parts of the body 
less accessible to the horse's mouth. 

Various nose protectors are in use against G. haemorrhoidalis^ but 
there are objections to many of them. A piece of leather suspended 
below the lips from the bit rings is simplest and best. For animals 
on pasture a halter with a box-like arrangement and throat cover has 
been devised to protect horses against infestation by all three species. 



50 BULLETIN 5d1, V. S. DEPARTMENT OF AGEICULTUEE. 

Kerosene oil used as a wash is ineffective in destroying the eggs 
of Gastrophihis, but certain other substances have given good results. 
Carbolic acid containing 2 per cent phenols is satisfactory for de- 
stroying eggs when applied to the infested parts of the host. 

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New Haven, 1908. 



PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF AGRI- 
CULTURE RELATING TO INSECTS AFFECTING THE HEALTH OF 
MAN AND DOMESTIC ANIMALS. 

AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT. 

Remedies and I'reveutives Against Mosquitoes. (Farmers' Bulletin 444.) 

Some Facts About Malaria. (Farmers' Bulletin 450.) 

The Sanitary I'rivy. (Farmers' Bulletin 403.) 

How to Prevent Typhoid Fever. (Farmers' Bulletin 478.) 

The Stable Fly. (Farmers' Bulletin 540.) 

The Yellow Fever Mosquito. (Farmers' Bulletin 547.) 

Harvest Mites, or " Chiggers." (Farmers' Bulletin 671.) 

The Bedbug. (Farmers' Bulletin 754.) 

Mites and Lice on Poultry. (Farmers' Bulletin 801.) 

The House Fly. (Farmers' Bulletin 851.) 

Screw^-Worms and Otlier Maggots Affecting Animals. (Farmers' Bulletin 857.) 

Fleas and Their Control. (Farmers' Bulletin 897.) 

Experiments in the Use of Sheep in tlie Eradication of the Rocky Mountain 
Spotted-Fever Tick. (Department Bulletin 45.) 

Fleas. (Department Bulletin 248.) 

Chicken Mite. (Department Bulletin 553.) 

Distribution of the Rocky Mountain Spotted-Fever Tick. (Entomology Cir- 
cular 136.) 

Hydrocyanic- Acid Gas Against Household Insects. (Farmers' Bulletin 699.) 

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING 
OFFICE, WASHINGTON. D. C. 

Notes on the Preoviposition Period of the House Fly. (Department Bulletin 

345.) 1916. Price, 5 cents. 
Experiments During 1915 in the Destruction of Fly Larvse in Horse Manure. 

(Department Bulletin 408.) Price, 5 cents. 
Ox "Warble. (Entomology Circular 25.) 1897. Price, 5 cents. 
Horn Fly. (Entomology Circular 115.) 1910. Price, 5 cents. 
The Fowl Tick. (Entomology Circular 170.) 1913. Price, 5 cents. 
Insects Affecting Domestic Animals. (Entomology Bulletin 5, n. s.) 1896. 

Price, 20 cents. 
Notes on Mos<iuitoes of the United States. (Entomology Bulletin 25, n, s.) 

1900. Price, 10 cents. 
Notes on " Punkies." (Entomology Bulletin 64, Pt. III.) 1907. Price, 5 cents. 
Information Concerning the North American Fever Tick, with Notes on Other 

Species. (Entomology Bulletin 72.) 1907. Price, 15 cents. 
Economic Loss to the People of the United States through Insects that Carry 

Disease. (Entomology Bulletin 78.) 1909. Price, 10 cents. 
Preventive and Remedial Work Against Mosquitoes. (Entomology Bulletin 88.) 

1910. Price, 15 cents. 
The Rocky Mountain Spotted-Fever Tick, with Special Reference to the Problem 

of Its Control in the Bitter Root Valley in Montana. (Entomology Bulletin 

105.) 1911. Price, 10 cents. 
The Life History and Bionomics of Some North American Ticks. (Entomology 

Bulletin 106.) 1912. Price, 30 cents. 
52 

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